DataSourceOVF: use util.find_devs_with(TYPE=iso9660)

DataSourceOVF attempts to find iso files via walking os.listdir('/dev/')
which is far too wide.  This approach is too invasive and can sometimes
race with systemd attempting to fsck and mount devices.

Instead, utilize cloudinit.util.find_devs_with to filter devices by
criteria (which uses blkid under the covers).  This results in fewer
attempts to mount block devices which do not contain iso filesystems.

Unittest changes include:
- cloudinit.tests.helpers; introduce add_patch() helper
- Add unittest coverage for DataSourceOVF use of transport_iso9660

LP: #1718287

1 files changed, 10 insertions, 0 deletions

diff --git a/cloudinit/tests/helpers.py b/cloudinit/tests/helpers.py
index 28e26622..6f88a5b7 100644
--- a/cloudinit/tests/helpers.py
+++ b/cloudinit/tests/helpers.py
@@ -104,6 +104,16 @@ class TestCase(unittest2.TestCase):
         super(TestCase, self).setUp()
         self.reset_global_state()
 
+    def add_patch(self, target, attr, **kwargs):
+        """Patches specified target object and sets it as attr on test
+        instance also schedules cleanup"""
+        if 'autospec' not in kwargs:
+            kwargs['autospec'] = True
+        m = mock.patch(target, **kwargs)
+        p = m.start()
+        self.addCleanup(m.stop)
+        setattr(self, attr, p)
+
 
 class CiTestCase(TestCase):
     """This is the preferred test case base class unless user