Make snapshots with qemu-img instead of libvirt

* snapshot is only supposed to snapshot the root drive, whereas
   libvirt snapshots snapshot the memory and all attached disks
 * removes silly qemu_img flag
 * fixes bug 946830

Change-Id: I6afc9dbaa855f06864cd5a37f89ad63555e35d23

nova/rootwrap/compute.py

@@ -179,6 +179,10 @@ filterlist = [
     # nova/virt/xenapi/vm_utils.py: 'mkfs'
     filters.CommandFilter("/sbin/mkfs", "root"),
 
+    # nova/virt/libvirt/utils.py: 'qemu-img'
+    filters.CommandFilter("/usr/bin/qemu-img", "root"),
+
     # nova/virt/libvirt/connection.py:
     filters.ReadFileFilter("/etc/iscsi/initiatorname.iscsi"),
+
     ]

nova/tests/fake_libvirt_utils.py

@@ -61,6 +61,14 @@ def chown(path, owner):
     pass
 
 
+def create_snapshot(disk_path, snapshot_name):
+    pass
+
+
+def delete_snapshot(disk_path, snapshot_name):
+    pass
+
+
 def extract_snapshot(disk_path, source_fmt, snapshot_name, out_path, dest_fmt):
     files[out_path] = ''
 

nova/tests/test_libvirt.py

@@ -96,8 +96,14 @@ class FakeVirtDomain(object):
     def name(self):
         return "fake-domain %s" % self
 
-    def snapshotCreateXML(self, *args):
-        return FakeVirDomainSnapshot(self)
+    def info(self):
+        return [power_state.RUNNING, None, None, None, None]
+
+    def create(self):
+        pass
+
+    def managedSave(self, *args):
+        pass
 
     def createWithFlags(self, launch_flags):
         pass