autotest: enable submodule build for binaries

Tools/scripts/build_all_px4.sh

@@ -8,6 +8,9 @@
 set -e
 set -x
 
+git submodule init
+git submodule update
+
 for d in ArduPlane ArduCopter APMrover2; do
     pushd $d
     make px4-clean

Tools/scripts/build_binaries.sh

@@ -289,6 +289,9 @@ build_antennatracker() {
 }
 
 # make sure PX4 is rebuilt from scratch
+git submodule init
+git submodule update
+
 pushd ArduPlane
 make px4-clean || exit 1
 popd