Fixed failed unit tests

1. Fixed a failed/flaky signal strength unit test caused
   by ag/2247950
2. Gracefully reset airplane mode settings in testCarrierActionResetOnAPM

Test: Telephony unit tests
bug: 29579544
Merged-In: I1108e62d1b970c5ac267173ea61afab9b78a624b
Change-Id: I1108e62d1b970c5ac267173ea61afab9b78a624b
(cherry picked from commit 53ea3cba)