autotest: use BATTERY_STATUS to detect sub reboot

Sub doesn't implement AP_Stats so we have custom reboot detection for
it.

The current look-for-string strategy is flawed - we're missing the
string on reboot

Tools/autotest/ardusub.py

@@ -3,6 +3,7 @@
 # Dive ArduSub in SITL
 from __future__ import print_function
 import os
+import time
 
 from pymavlink import mavutil
 
@@ -326,16 +327,43 @@ class AutoTestSub(AutoTest):
 
     def reboot_sitl(self):
         """Reboot SITL instance and wait it to reconnect."""
-        self.context_push()
-        self.context_collect("STATUSTEXT")
-        self.send_reboot_command()
-        # "Init ArduSub" comes out as raw text, not a statustext
-        for i in range(2):
+        # out battery is reset to full on reboot.  So reduce it to 10%
+        # and wait for it to go above 50.
+        self.run_cmd(mavutil.mavlink.MAV_CMD_BATTERY_RESET,
+                     255,  # battery mask
+                     10,  # percentage
+                     0,
+                     0,
+                     0,
+                     0,
+                     0,
+                     0)
+        self.run_cmd_reboot()
+        tstart = time.time()
+        while True:
+            if time.time() - tstart > 30:
+                raise NotAchievedException("Did not detect reboot")
+            # ask for the message:
+            batt = None
             try:
-                self.wait_statustext("ArduPilot Ready", check_context=True, wallclock_timeout=True)
+                self.send_cmd(mavutil.mavlink.MAV_CMD_REQUEST_MESSAGE,
+                              mavutil.mavlink.MAVLINK_MSG_ID_BATTERY_STATUS,
+                              0,
+                              0,
+                              0,
+                              0,
+                              0,
+                              0)
+                batt = self.mav.recv_match(type='BATTERY_STATUS',
+                                           blocking=True,
+                                           timeout=1)
             except ConnectionResetError as e:
                 pass
-        self.context_pop()
+            self.progress("Battery: %s" % str(batt))
+            if batt is None:
+                continue
+            if batt.battery_remaining > 50:
+                break
         self.initialise_after_reboot_sitl()
 
     def apply_defaultfile_parameters(self):

Tools/autotest/common.py

@@ -1488,6 +1488,17 @@ class AutoTest(ABC):
             backup_valgrind_log = ("%s-%s" % (str(int(time.time())), valgrind_log))
             shutil.move(valgrind_log, backup_valgrind_log)
 
+    def run_cmd_reboot(self):
+        self.run_cmd(mavutil.mavlink.MAV_CMD_PREFLIGHT_REBOOT_SHUTDOWN,
+                     1,  # confirmation
+                     1,  # reboot autopilot
+                     0,
+                     0,
+                     0,
+                     0,
+                     0,
+                     0)
+
     def reboot_sitl_mav(self, required_bootcount=None):
         """Reboot SITL instance using mavlink and wait for it to reconnect."""
         old_bootcount = self.get_parameter('STAT_BOOTCNT')
@@ -1500,15 +1511,7 @@ class AutoTest(ABC):
             self.start_SITL(wipe=False)
         else:
             self.progress("Executing reboot command")
-            self.run_cmd(mavutil.mavlink.MAV_CMD_PREFLIGHT_REBOOT_SHUTDOWN,
-                         1,  # confirmation
-                         1,  # reboot autopilot
-                         0,
-                         0,
-                         0,
-                         0,
-                         0,
-                         0)
+            self.run_cmd_reboot()
         self.detect_and_handle_reboot(old_bootcount, required_bootcount=required_bootcount)
 
     def send_cmd_enter_cpu_lockup(self):