Tools: make Python import error more readable

The problem with printing the exception was that starting with
Python 3.6 the ImportError is yet another (sub) exception called
ModuleNotFoundError which can't be printed as a string and then triggers
another exception:

```
Traceback (most recent call last):
  File "/home/julianoes/src/Firmware/Tools/serial/generate_config.py", line 11, in <module>
    import jinja2
ModuleNotFoundError: No module named 'jinja2'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/julianoes/src/Firmware/Tools/serial/generate_config.py", line 13, in <module>
    print("Failed to import jinja2: " + e)
TypeError: must be str, not ModuleNotFoundError
```

As per @bkueng's suggestion the easiest is to cast the exception to str
and that way prevent the second exception.

Tools/mavlink_shell.py

@@ -16,7 +16,7 @@ from argparse import ArgumentParser
 try:
     from pymavlink import mavutil
 except ImportError as e:
-    print("Failed to import pymavlink: " + e)
+    print("Failed to import pymavlink: " + str(e))
     print("")
     print("You may need to install it with:")
     print("    pip3 install --user pymavlink")
@@ -26,7 +26,7 @@ except ImportError as e:
 try:
     import serial
 except ImportError as e:
-    print("Failed to import pyserial: " + e)
+    print("Failed to import pyserial: " + str(e))
     print("")
     print("You may need to install it with:")
     print("    pip3 install --user pyserial")

Tools/mavlink_ulog_streaming.py

@@ -17,7 +17,7 @@ from argparse import ArgumentParser
 try:
     from pymavlink import mavutil
 except ImportError as e:
-    print("Failed to import pymavlink: " + e)
+    print("Failed to import pymavlink: " + str(e))
     print("")
     print("You may need to install it with:")
     print("    pip3 install --user pymavlink")

Tools/serial/generate_config.py

@@ -10,7 +10,7 @@ import sys
 try:
     from jinja2 import Environment, FileSystemLoader
 except ImportError as e:
-    print("Failed to import jinja2: " + e)
+    print("Failed to import jinja2: " + str(e))
     print("")
     print("You may need to install it using:")
     print("    pip3 install --user jinja2")
@@ -20,7 +20,7 @@ except ImportError as e:
 try:
     import yaml
 except ImportError as e:
-    print("Failed to import yaml: " + e)
+    print("Failed to import yaml: " + str(e))
     print("")
     print("You may need to install it using:")
     print("    pip3 install --user pyyaml")

Tools/upload_log.py

@@ -17,7 +17,7 @@ import sys
 try:
     import requests
 except ImportError as e:
-    print("Failed to import requests: " + e)
+    print("Failed to import requests: " + str(e))
     print("")
     print("You may need to install it using:")
     print("    pip3 install --user requests")

Tools/validate_yaml.py

@@ -4,13 +4,12 @@
 from __future__ import print_function
 
 import argparse
-import os
 import sys
 
 try:
     import yaml
 except ImportError as e:
-    print("Failed to import yaml: " + e)
+    print("Failed to import yaml: " + str(e))
     print("")
     print("You may need to install it using:")
     print("    pip3 install --user pyyaml")
@@ -20,7 +19,7 @@ except ImportError as e:
 try:
     import cerberus
 except ImportError as e:
-    print("Failed to import cerberus: " + e)
+    print("Failed to import cerberus: " + str(e))
     print("")
     print("You may need to install it using:")
     print("    pip3 install --user cerberus")

msg/tools/px_generate_uorb_topic_files.py

@@ -43,31 +43,26 @@ import shutil
 import filecmp
 import argparse
 import sys
-import errno
 
 try:
     import em
 except ImportError as e:
-    print("Python import error: ", e)
-    print('''
-Required python package empy not installed.
-
-Please run:
-    pip3 install --user empy
-''')
-    exit(1)
+    print("Failed to import em: " + str(e))
+    print("")
+    print("You may need to install it using:")
+    print("    pip3 install --user empy")
+    print("")
+    sys.exit(1)
 
 try:
     import genmsg.template_tools
 except ImportError as e:
-    print("Python import error: ", e)
-    print('''
-Required python package pyros-genmsg not installed.
-
-Please run:
-    pip3 install --user pyros-genmsg
-''')
-    exit(1)
+    print("Failed to import genmsg: " + str(e))
+    print("")
+    print("You may need to install it using:")
+    print("    pip3 install --user pyros-genmsg")
+    print("")
+    sys.exit(1)
 
 
 __author__ = "Sergey Belash, Thomas Gubler, Beat Kueng"

src/lib/mixer/MultirotorMixer/geometries/tools/px_generate_mixers.py

@@ -37,28 +37,34 @@ px_generate_mixers.py
 Generates c/cpp header/source files for multirotor mixers
 from geometry descriptions files (.toml format)
 """
+import sys
 
 try:
     import toml
+except ImportError as e:
+    print("Failed to import toml: " + str(e))
+    print("")
+    print("You may need to install it using:")
+    print("    pip3 install --user toml")
+    print("")
+    sys.exit(1)
+
+try:
     import numpy as np
 except ImportError as e:
-    print("python import error: ", e)
-    print('''
-Required python3 packages not installed.
-
-On a GNU/Linux or MacOS system please run:
-  sudo pip3 install numpy toml
-
-On Windows please run:
-  easy_install numpy toml
-''')
-    exit(1)
+    print("Failed to import numpy: " + str(e))
+    print("")
+    print("You may need to install it using:")
+    print("    pip3 install --user numpy")
+    print("")
+    sys.exit(1)
 
 __author__ = "Julien Lecoeur"
 __copyright__ = "Copyright (C) 2013-2017 PX4 Development Team."
 __license__ = "BSD"
 __email__ = "julien.lecoeur@gmail.com"
 
+
 def parse_geometry_toml(filename):
     '''
     Parses toml geometry file and returns a dictionary with curated list of rotors

src/lib/parameters/px_generate_params.py

@@ -11,7 +11,7 @@ import sys
 try:
     from jinja2 import Environment, FileSystemLoader
 except ImportError as e:
-    print("Failed to import jinja2: " + e)
+    print("Failed to import jinja2: " + str(e))
     print("")
     print("You may need to install it using:")
     print("    pip3 install --user jinja2")