Revert "Use debug level logging during unit tests"

This change made the subunit_log 190 MB on every run (14MB
in the gz version). It also dramatically increases the
memory needed to run unit tests. We need to revert and
come at this problem with fresh eyes to address the problem
at hand without effectively overrunning people's environments.

This reverts commit f9090b0bd796f8c2fdf8d0a23173f3adee71b3df.

Change-Id: Ia1cfc3d874ddf4f8ee2037b487d22f968585854e
(cherry picked from commit f350f24cd2bad0d62a737c0f100e40cdfbbb36f6)