Indicating the location tests directory in oslo_debug_helper
Indicating the location tests directory in oslo_debug_helper

According to [1], we can passing a "-t" argument to
oslo_debug_helper to indicate the directory where tests
are located. This will solves ImportError exception.

[1] https://docs.openstack.org/developer/oslotest/features.html

Change-Id: I1b6b965f5e999aac85adf97ac7c0cb0a0edce41e
Closes-Bug: #1666560

openstack/sahara,openstack/sahara