Refactor libvirt create calls

* minimizes duplicated code for create
 * makes wait_for_destroy happen on shutdown instead of undefine
 * allows for destruction of an instance while leaving the domain
 * uses reset for hard reboot instead of create/destroy
 * makes resume_host_state use new methods instead of hard_reboot
 * makes rescue/unrescue not use hard reboot to recreate domain

Change-Id: I2072f93ad6c889d534b04009671147af653048e7

nova/tests/fakelibvirt.py

@@ -288,6 +288,11 @@ class Domain(object):
         self._state = VIR_DOMAIN_SHUTDOWN
         self._connection._mark_not_running(self)
 
+    def reset(self, flags):
+        # FIXME: Not handling flags at the moment
+        self._state = VIR_DOMAIN_RUNNING
+        self._connection._mark_running(self)
+
     def info(self):
         return [self._state,
                 long(self._def['memory']),