Implement get_hypervisor_hostname for libvirt.

Implements get_hypervisor_hostname so that the
OS-EXT-SRV-ATTR:hypervisor_hostname extension can properly
display this information when using libvirt.

Fixes LP Bug #999729.

Change-Id: I124d48ca352dc225f88999046f9d212ffb9e4c6e

nova/tests/fakelibvirt.py

@@ -507,6 +507,9 @@ class Connection(object):
     def getVersion(self):
         return 14000
 
+    def getHostname(self):
+        return 'compute1'
+
     def getCapabilities(self):
         return '''<capabilities>
   <host>

nova/tests/test_libvirt.py

@@ -1695,6 +1695,9 @@ class HostStateTestCase(test.TestCase):
         def get_hypervisor_version(self):
             return 13091
 
+        def get_hypervisor_hostname(self):
+            return 'compute1'
+
         def get_disk_available_least(self):
             return 13091
 
@@ -1721,6 +1724,7 @@ class HostStateTestCase(test.TestCase):
         self.assertEquals(stats["host_memory_free"], 409)
         self.assertEquals(stats["hypervisor_type"], 'QEMU')
         self.assertEquals(stats["hypervisor_version"], 13091)
+        self.assertEquals(stats["hypervisor_hostname"], 'compute1')
 
 
 class NWFilterFakes: