CA-148243: Getting rid of bad assertion failures during VM lifecycle
operations

Issue: After a VM lifecycle operation, assert statement throws assertion
failure in an ugly manner.

Fix: Removing the assert statements and replacing them with
vm_bad_power_state error in case the power state of VM doesn't match the
expected state after some lifecycle operation.

Signed-off-by: Ravi Pandey <ravi.pandey@citrix.com>