Skip snapshot test when missing qemu-img

Since the commit the remove AMI snapshot format special casing
has merged, we're now running the libvirt snapshot tests as expected.
However, for those tests qemu-img binary needs to be installed.
Because these tests have been silently and incorrectly skipped for so long,
they didn't receive the same maintenance as other tests as the failures went unnoticed.

Change-Id: Ia90eedbe35f4ab2b200bdc90e0e35e5a86cc2110
Closes-bug: #2075178
Signed-off-by: Julien Le Jeune <julien.le-jeune@ovhcloud.com>
(cherry picked from commit 0809f75d79)

nova/tests/unit/virt/test_virt_drivers.py

@@ -21,6 +21,7 @@ import fixtures
 import netaddr
 import os_resource_classes as orc
 import os_vif
+from oslo_concurrency import processutils
 from oslo_log import log as logging
 from oslo_serialization import jsonutils
 from oslo_utils import importutils
@@ -239,8 +240,16 @@ class _VirtDriverTestCase(_FakeDriverBackendTestCase):
     def test_snapshot_running(self):
         img_ref = self.image_service.create(self.ctxt, {'name': 'snap-1'})
         instance_ref, network_info = self._get_running_instance()
+        # this test depends on qemu-img
+        # being installed and in the path,
+        # if it is not installed, skip
+        try:
             self.connection.snapshot(self.ctxt, instance_ref, img_ref['id'],
                                      lambda *args, **kwargs: None)
+        except processutils.ProcessExecutionError as e:
+            if 'qemu-img' in e.stderr and 'No such file' in e.stderr:
+                self.skipTest("qemu-img not installed")
+            raise e
 
     @catch_notimplementederror
     def test_reboot(self):