This commit adds the following variables to os_tempest role:
tempest_volume_backend1_name
tempest_volume_backend2_name
tempest_volume_multi_backend_enabled
This allows you to test that using multiple cinder backends
simultaneously works as expected. A deployer may, for example, set
tempest_volume_backend1_name to 'lvm' and tempest_volume_backend2_name
to 'ceph'.
To avoid any surprises, tempest_volume_multi_backend_enabled defaults to
'False', which is the current tempest default value for multi_backend.
Closes-Bug: #1493911
Change-Id: I5eeb88d3e90b6ca046be96fb61a1cb6f4e6087ee
ed4ed6aa20