Move ssh|ping-able server logic into separate method

We can use the ssh|ping-able logic into many other tests than
just in common create server method. For example, when in rescue
server negative test, we need to check for SSH after test unrescue
the server and detach volume from it.

Change-Id: Ibc59e03c7f6a0aa89fb6188a5cb68be39c3ee611
1 file changed