logcat: unit test produces log stutter

logd now counts multiple identical messages, causing messages to be
held back.  Stop doing that in the tests.  When that filter appeared,
the logcat-unit-tests went from 23 seconds to a couple of minutes of
runtime breakign the automated testing.

Test: gTest logcat-unit-tests total time less than 1 minute.
Bug: 33845198
Bug: 33535908
Change-Id: I6145bae89b6d5e5024ef4f8fe66440c9ae53f7c6