During end to end testing, the system load on some devices may be
high enough to cause the scheduler to not give audio_core another
time slice, leading to UNDERFLOW conditions.  This is causing
failures in CI.

BUG: MTWN-269
TEST: Ran end to end test repeatedly with no failures.
Change-Id: I3b0cc24140b88bf9315abddf59a461491d504d53