1. Test whether start tethering is gated by suitable permission.
2. Test stopAllTethering
Bug: 153613718
Test: atest CtsTetheringTest
Change-Id: I38702886ea355e1aec8eb8ac404fdd46a44582e3
Initial CTS test for tethering.
This change test startTethering/stopTethering and check
status of TETHER_STATE_CHANGE intent.
Bug: 145490751
Test: atest CtsTetheringTest
Change-Id: Ia1ae3b6c2b68b009ca4deef840945186d472d99e