Fix loading instance fault in servers view

If VM schedule failed, then VM will be set to ERROR state,
but "nova show" does not show the fault of the VM.

The fix use lazy load to get instance fault if the instance
went to ERROR state.

Closes-Bug: #1212915

Change-Id: If286fd0176be8307c50b2a7c3534fff33fa5c10f
Merge "Fix loading instance fault in servers view"