Add ability to skip log capture.

Change-Id: I8f3ac5c469e9d530d1ac7776c7488d0c42cdf1ad
Reviewed-on: https://review.openstack.org/35329
Approved: James E. Blair <corvus@inaugust.com>
Reviewed-by: James E. Blair <corvus@inaugust.com>
Tested-by: Jenkins