Fix suppressed CallDetailsActivityTest tests.

A recent change that marked voicemails as read when call details page is
opened broke callDetailsActivityTest because it used arbitrary fake
voicemail uri which never matched a valid content provider.

The offending tests were suppressed subsequently.

This change modifies the fake_uri to be built out of voicemail content
uri, but does not point to any real entry.

testVoicemailPlaybackRateDisplayedOnUi still fails due to an unrelated
change. This is still suppressed. Other tests have been unsupprressed.

Change-Id: Ie25a44f3cfc7263d9b127aa33f467a57eae07af7