Add ability to simulate missed calls

After initiating a call using
adb shell am start -a android.telecom.testapps.ACTION_START_INCOMING_CALL
-d "tel:14082932268"

Hang up the call using:
adb shell am start -a android.telecom.testapps.ACTION_HANGUP_CALLS

Bug: 19803865

Change-Id: I913666dc45ea518f4f95a321121680fb7aabbb6f