Fixed Sound Settings summary text

The summary for Sound settings was not
descriptive enough when the volume was set
to 0% so additional strings were added. Now
it will change let you know the status
of the ringer and vibration settings when
at 0% volume. Espresso tests added to test
that text is properly updated in each of
these states.

Test: make SettingsTests
Bug: 31099179
Change-Id: Id49e2d0c4b7ac0f17efcdaf31de48d5eb678ca46