Make default dialer tests less flaky

If a test was ended unexpectedly (e.g. process termination or
system crash), the default dialer would remain set as the test app.

This would lead to cascading test failures which were a result of assuming
that the test app wasn't the default dialer at the start of the app.

To fix this, reset the default dialer to the system dialer (which is
our best effort guess at a dialer that is still installed on the
device) before starting each test.

Also, make sure to skip tests for devices that don't support Telephony.
This was causing test failures for tablets which did not have a
system dialer installed.

Bug: 20303674
Change-Id: I3426d4c528602ae7efdd97b65e3e903a16be07ed
3 files changed