Add wrapper for requests get in tls barbican tests

use validate_URL_response method for querying lb url in
barbican tests, because it allows to have retries on connection timeout.

Related-Prod: https://mirantis.jira.com/browse/PRODX-9013
Change-Id: I6ca75d975e22d1dd406fba46c845019678ec6cad
1 file changed