Fix that DISTRO is not set in unstack.sh
Fix that DISTRO is not set in unstack.sh

Change-Id: I36cab41fdb767e8e31073a4fa1f929090f702910
Closes-Bug: #1738938

group-policy/devstack,noironetworks/devstack,nawawi/openstack,noironetworks/devstack,group-policy/devstack,openstack-dev/devstack,dtroyer/devstack,openstack-dev/devstack,dtroyer/devstack,nawawi/openstack