tempest: configure compute-feature-enabled.swap_volume if libvirt
tempest: configure compute-feature-enabled.swap_volume if libvirt

The only virt driver in nova that supports the swap volume API is
libvirt so enable testing that in Tempest only if using libvirt.

Depends on two changes:

1. The Tempest change that adds the new config option and test.

Depends-On: I2d4779de8d21aa84533f4f92d347e932db2de58e

2. A nova fix for correctly waiting for the block copy job in the guest
   to complete.

Depends-On: I0c52917a5555a70c4973f37dea1aebf878dd73b4

Change-Id: Ibb6b309574d2c6a06fcecb0626ea21527fb7f412

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