openstack: retry if volume create+attach operation fails

openstack: retry if volume create+attach operation fails

Once in awhile, a created volume fails to become available within
a reasonable period of time. When this happens, the entire test job
fails with the following error:

2018-10-02T06:52:44.106 ERROR:teuthology.provision.openstack:'volume
target192168000058-2' reached maximum tries (100) after waiting for 200
seconds

With this commit, we catch that exception and retry with a new volume.

Signed-off-by: Nathan Cutler <ncutler@suse.com>
Signed-off-by: Kyrylo Shatskyy <kyrylo.shatskyy@suse.com>
Conflicts:
	teuthology/provision/openstack.py