Fix intermittent transient cluster tests failure

Getting cluster_info, after we created transient cluster and run a job
on it, might fail if cluster was terminated by periodic before that.
On the other hand, we only need cluster_id from the cluster_info, which
we already have. For example see the following test run:

https://sahara.mirantis.com/logs/22/93322/1/check/gate-sahara-integration-transient/e03a813/console.html

Change-Id: I1efa4da87ebcbfbcd5d04f9b8eaf3b218562b8d1