adb_wait_for_device: If we can't get the battery level, just exit

platform_tools/android/bin/adb_wait_for_device

 #!/bin/bash
 #
 # Wait for the device to be ready to run tests.
 
 SCRIPT_DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
 source $SCRIPT_DIR/android_setup.sh
 source $SCRIPT_DIR/utils/setup_adb.sh
 
 function get_battery_level {
   STATS="$($ADB $DEVICE_SERIAL shell dumpsys batteryproperties)"
   SPLIT=( $STATS )
   for i in "${!SPLIT[@]}"; do
     if [ "${SPLIT[$i]}" = "level:" ]; then
       echo "${SPLIT[$i+1]}"
       return
     fi
   done
   echo "Could not determine battery level!" 1>&2
-  echo "0"
+  # Just exit to prevent hanging forever or failing the build.
+  exit 0
 }
 
 set -e
 
 # Wait for the device to be connected and fully booted.
 while [ "$($ADB $DEVICE_SERIAL shell getprop sys.boot_completed | tr -d '\r')" != "1" ]; do
   echo "Waiting for the device to be connected and ready."
   sleep 5
 done
 
 # Wait for battery charge.
 DESIRED_BATTERY_LEVEL=30
 CURRENT_BATTERY_LEVEL="$(get_battery_level)"
 while [ "${CURRENT_BATTERY_LEVEL}" -lt "${DESIRED_BATTERY_LEVEL}" ]; do
   echo "Battery level is ${CURRENT_BATTERY_LEVEL}; waiting to charge to ${DESIRED_BATTERY_LEVEL}"
   sleep 5
   CURRENT_BATTERY_LEVEL="$(get_battery_level)"
 done
 
 echo "Ready!"