Always record kati stats into soong log

Pass --dump-stats to ckati, but filter out the '*kati*' lines so that
they only end up in our verbose output. That way we've always got access
to the statistics.

Bug: 36182021
Test: m nothing; cat out/soong.log
Change-Id: Iaf7a814fc67f3e475c913faf69924a7f4e2ae3b3