Remove unnecessary returns

* remove duplicated xtrace
* remove some unnecessary return

Change-Id: If9e0a979e0bd5a334e82d42572ac0b149de341d7
Turn off tenant_isolation in tempest for quantum

Current tempest didn't create networks for each tenant, so let
tempest use demo tenant for tesing if we enable quantum.

Change-Id: I5f139b5f1bdf5c176130b8db9e896e2cb48b4420
Clean up cinder volume group rather than remove it

Removing the cinder volume group breaks devstack installations
that share that volume group with other logical volumes. It also was
leaking loopback devices.

Change-Id: Ice4470e06e08ce49a0e1f82af70abcc015c91c20
Merge "Turn off tenant_isolation in tempest for quantum"
Merge "Remove unnecessary returns"
Merge "Clean up cinder volume group rather than remove it"