Migrated unit tests and added debug messages

Added debug messages in keepalive tracker. Also
ported the unit tests from DataConnectionTest. Also
removed the unnecessary waiting after using testable
looper.

Bug: 214234027
Test: atest KeepAlivetrackerTest
Change-Id: Ic69a599e609240377dbce2d0b3dca53238035d8e
Merged-In: Ic69a599e609240377dbce2d0b3dca53238035d8e