WifiConnectivityManager: Unit tests for rate limit

Adding unit tests to verify the connection attempt rate limiting
functionality. Had to change the way system time is being fetched in
WifiConnectivityManager to achieve this.

BUG: 28242396
Change-Id: I2bfae3a9ea60cba1c3c1405dd5eb58208f12c2db
TEST: Compiles & unit-test passes
5 files changed
tree: 22675cded2dc6202fdba4dbfbcaa1353e28a8ae0
  1. service/
  2. tests/