VMware: remove duplicate _fake_create_session code

This patch pulls the _fake_create_session method out so it can be reused
across tests rather than duplicated it.

Change-Id: Ie3979a84568571b2f1f63e01c6c5fb6966f0333a
Closes-bug: 1312472
Merge "VMware: remove duplicate _fake_create_session code"