Downgrade InputMethodManager getFallbackIMM logs

Previously the IMM was logging error and warning logs every single time
it attempted to use an IMM method and ended up with the fallback IMM.
This is both extremely noisy since the IMM is accessed multiple times
per second in the case of the user typing and a little misleading since
this isn't truly an error condition on its own.

Downgrade the log to a VERBOSE log. This will still show up for apps
when in development but is less likely to wander into bug reports for
released apps.

Bug: 141884160
Fixes: 141884160
Test: Manually. Trigerred error condition and verified log level.

Change-Id: If25ef81c6b74679ebfa725f0c98e0bc633399e70