Disable compute interface attach Tempest tests if using cells
Disable compute interface attach Tempest tests if using cells

Cells doesn't support the os-attach-interfaces API so disable those
tests in Tempest if running with Cells.

Change-Id: I5c7884407868eae70ea125f3f893c73214c04c75

bigswitch/devstack,prithivm/branch01,openstack-dev/devstack,noironetworks/devstack,dirkmueller/devstack,pombredanne/devstack,dirkmueller/devstack,openstack-dev/devstack,noironetworks/devstack,bswartz/devstack,Mahito/devstack,prithivm/branch01,bswartz/devstack,bigswitch/devstack,group-policy/devstack,thomasem/devstack,samgoon/devstack,richliu/devstack,richliu/devstack,group-policy/devstack,mssumanth/devstack,samgoon/devstack,nawawi/openstack,dtroyer/devstack,mssumanth/devstack,avvocatodemarchis/devstack,Mahito/devstack,dtroyer/devstack,varunarya10/devstack,nawawi/openstack,varunarya10/devstack,pombredanne/devstack,avvocatodemarchis/devstack,thomasem/devstack