Simplify test force delete snapshot unit test

Make this test simple in just verifying if we have a snapshot and we do
a force delete that we get back an ok response from the controller.
Removing out RPC call and verifying snapshot was deleted since that's
out of the scope here.

Closes-Bug: #1291108
Change-Id: If10b1057cf170e77527a0933a1ddf1a6a59baa1d
Merge "Simplify test force delete snapshot unit test"