Start foreground service from ConnectivityBackgroundTestActivity

On TV, CtsVerifier is moved to background and gets frozen when the
screen is off.
This makes ConnectivityBackgroundTest fails since CtsVerifier can not
continue connectivity test while it's frozen.
This CL adds a foreground service and avoids CtsVerifier is being
frozen.

Test: CtsVerifier
Bug: 284060686
Change-Id: If3c3edfd5f18bd8eb193676a0e009995b5e45ccd
3 files changed