Fixes hypervisor based image filtering on Hyper-V

Fixes Bug #1073547

Nova scheduler's ImagePropertiesFilter based filtering requires the
"supported_instances" stat returned by the driver's get_host_stats method.
This fix implements the get_host_stats method, providing also some
refactoring in the process by adding a HostOps class.

Change-Id: Ia6e73eb3e8ff0be028854fe4fd6d8e305fa1d504

nova/tests/test_hypervapi.py

@@ -103,6 +103,7 @@ class HyperVAPITestCase(basetestcase.BaseTestCase):
 
         # Modules in which the mocks are going to be injected
         from nova.virt.hyperv import baseops
+        from nova.virt.hyperv import hostops
         from nova.virt.hyperv import livemigrationops
         from nova.virt.hyperv import snapshotops
         from nova.virt.hyperv import vmops
@@ -112,6 +113,7 @@ class HyperVAPITestCase(basetestcase.BaseTestCase):
         modules_to_test = [
             driver_hyperv,
             baseops,
+            hostops,
             vmops,
             vmutils,
             volumeops,
@@ -157,6 +159,14 @@ class HyperVAPITestCase(basetestcase.BaseTestCase):
 
         self.assertEquals(dic['hypervisor_hostname'], platform.node())
 
+    def test_get_host_stats(self):
+        dic = self._conn.get_host_stats(True)
+
+        self.assertEquals(dic['disk_total'],
+            dic['disk_used'] + dic['disk_available'])
+        self.assertEquals(dic['host_memory_total'],
+            dic['host_memory_overhead'] + dic['host_memory_free'])
+
     def test_list_instances(self):
         num_vms = self._hypervutils.get_vm_count()
         instances = self._conn.list_instances()