Allow DHSS=False tests to override Tempest concurrency
Allow DHSS=False tests to override Tempest concurrency

The post_test_hook.sh script was hardcoding the Tempest concurrency
setting to 8 for DHSS=False test runs.  This patch has it honor the
MANILA_TEMPEST_CONCURRENCY environment variable, if it exists.

Change-Id: Ia2f0495560517484ba4d9290ced2c4dc3de6fb34
Closes-bug: 1546150

vponomaryov/manila,NetApp/manila,NetApp/manila,openstack/manila,vponomaryov/manila,bswartz/manila,openstack/manila,bswartz/manila