Adding a shell command to AlarmManager

Adding a command to get the config version number which is incremented
everytime onPropertiesChanged is called. This is useful in waiting till
a change has been propagated to the service before proceeding with
tests.

Test: adb shell dumpsys alarm
adb shell cmd alarm get-config-version

Bug: 182835530
Change-Id: I171578255d4b69e75f535fd44ab0f5f462ea8d0b