Use OS_CMP format for compute ips

Use OS_CMP format for compute ips

The devstackutils library now will generate proper ips
for our OS_CMP1_IP and OS_CMP2_IP variables depending
on the deployment. In the case of an all-in-one deployment
the CMP1 and CMP2 ips are going to be the same. That
was done for all other suites back when we moved to this
method, but I think elan was missed somehow.

example of how it fails:
https://logs.opendaylight.org/releng/vex-yul-odl-jenkins-1/netvirt-csit-1node-1cmb-0ctl-0cmp-openstack-queens-upstream-stateful-fluorine/116/robot-plugin/log_full.html.gz#s1-s11-k1-k2-k7-k1-k5-k3-k1

you can see that the ssh session had no destination ip
listed, because that variable used was not available

Change-Id: I3cb2f63828bad2ee1fd4f3a03ce08eab30159295
Signed-off-by: Jamo Luhrsen <jluhrsen@redhat.com>