Fix various issues with the logger-test
Fix various issues with the logger-test

1) Unset all variables which affect how the logger work
   before running the test case

2) Use gtest macros instead of cb_assert

Change-Id: I3af619b9c04cdb126e84f7d47b119ef5436f9ada
Reviewed-on: http://review.couchbase.org/83953
Reviewed-by: Dave Rigby <a09264da4832c7ff1d3bf1608a19f4b870f93750@couchbase.com>
Tested-by: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>

daverigby/kv_engine,daverigby/kv_engine,daverigby/kv_engine,daverigby/kv_engine