Fix bugs in resource tracker and cleanup

Fixes bugs in resource tracker:
* Handle disk oversubscription
* Handle suspended/powered off instances

The usage model is changed to the old style that is
based on actual instance usage on a compute host.
(Not the current point in time of the hypervisor's
 reported host stats)

There is now a 'limits' filter property that can be passed from
the scheduler to the compute node to indicate that
oversubscription of resources is desired:

The 'limits' filter property is a dict with the following possible
keys:

* memory_mb - Specifies the memory ceiling for the compute node.
* disk_gb - Specifies the disk space ceiling for the compute node.
* vcpu - Specifies the max number of vcpus for the compute node.

There is also some general cleanup and additional unit tests in
an attempt to simplify down this function.

bug 1048842
bug 1052157

Change-Id: I6ee851b8c03234a78a64d9f5c494dfc7059cdda4

nova/compute/manager.py

@@ -251,8 +251,7 @@ def _instance_update(self, context, instance_uuid, **kwargs):
 
         (old_ref, instance_ref) = self.db.instance_update_and_get_original(
                 context, instance_uuid, kwargs)
-        self.resource_tracker.update_load_stats_for_instance(context,
-                instance_ref)
+        self.resource_tracker.update_usage(context, instance_ref)
         notifications.send_update(context, old_ref, instance_ref)
 
         return instance_ref
@@ -480,10 +479,14 @@ def _run_instance(self, context, request_spec,
             network_info = self._allocate_network(context, instance,
                                                   requested_networks)
             try:
-                memory_mb_limit = filter_properties.get('memory_mb_limit',
-                        None)
-                with self.resource_tracker.instance_resource_claim(context,
-                        instance, memory_mb_limit=memory_mb_limit):
+                limits = filter_properties.get('limits', {})
+                with self.resource_tracker.resource_claim(context, instance,
+                        limits):
+                    # Resources are available to build this instance here,
+                    # mark it as belonging to this host:
+                    self._instance_update(context, instance['uuid'],
+                            host=self.host, launched_on=self.host)
+
                     block_device_info = self._prep_block_device(context,
                             instance)
                     instance = self._spawn(context, instance, image_meta,
@@ -684,7 +687,6 @@ def _start_building(self, context, instance):
         LOG.audit(_('Starting instance...'), context=context,
                   instance=instance)
         self._instance_update(context, instance['uuid'],
-                              host=self.host, launched_on=self.host,
                               vm_state=vm_states.BUILDING,
                               task_state=None,
                               expected_task_state=(task_states.SCHEDULING,
@@ -889,8 +891,6 @@ def _delete_instance(self, context, instance):
         self.db.instance_destroy(context, instance_uuid)
         system_meta = self.db.instance_system_metadata_get(context,
             instance_uuid)
-        # mark resources free
-        self.resource_tracker.free_resources(context)
         self._notify_about_instance_usage(context, instance, "delete.end",
                 system_metadata=system_meta)