Fix two functional tests within tempest_plugin

Couple of functional tests within tempest plugin are generic driver specific,
it verifies API actions of security-services, but for reproducing test cases
tries create shares and share creation fails if enabled backend driver raises
exception in case security-service has fake/improper data.

Change-Id: Ib8915f1f7d52a6abc2f34cac4bba18a6ad7eaf46
Closes-Bug: #1371552