The list-agents rally test for nova was removed in wallaby, but it
was also only supported by the XenAPI hypervisor driver. We have
specifically overriden it for newer releases of openstack, but
with its removal and the specific driver usage, there's no real
need to keep it around.
Change-Id: I056b397444e8dc5d4b256a6fe03c23b53a0c0fff
d044c0cf3d