Merge ~smoser/curtin:fix/no-use-assert-called into curtin:master

[Scott Moser]

tests: replace usage of mock.assert_called

assert_called is only in mock 2 or newer, meaning this was failing
to run tests in a xenial build environment.

So just replace assert_called usage with assertTrue(mymock.called).

see commit message

[Ryan Harper (raharper)]

Good fix.

review: Approve

[Server Team CI bot (server-team-bot)]

PASSED: Continuous integration, rev:f39007a27555be5a1c8c0ceb1130cffe23bb70ac
https://jenkins.ubuntu.com/server/job/curtin-ci/941/
Executed test runs:
    SUCCESS: https://jenkins.ubuntu.com/server/job/curtin-ci/nodes=metal-amd64/941
    SUCCESS: https://jenkins.ubuntu.com/server/job/curtin-ci/nodes=metal-arm64/941
    SUCCESS: https://jenkins.ubuntu.com/server/job/curtin-ci/nodes=metal-ppc64el/941
    SUCCESS: https://jenkins.ubuntu.com/server/job/curtin-ci/nodes=metal-s390x/941

Click here to trigger a rebuild:
https://jenkins.ubuntu.com/server/job/curtin-ci/941/rebuild

review: Approve (continuous-integration)

[Scott Moser (smoser)]

An upstream commit landed for this bug.

To view that commit see the following URL:
https://git.launchpad.net/curtin/commit/?id=ae48e86f

diff --git a/tests/unittests/test_commands_block_meta.py b/tests/unittests/test_commands_block_meta.py
index 17186d4..a6a0b13 100644
--- a/tests/unittests/test_commands_block_meta.py
+++ b/tests/unittests/test_commands_block_meta.py
@@ -680,7 +680,7 @@ class TestFstabData(CiTestCase):
             call(['mount', "-t", "ext4", "-o", "defaults",
                   "/dev/disk1", "/mnt"], capture=True),
             m_subp.call_args)
-        m_ensure_dir.assert_called()
+        self.assertTrue(m_ensure_dir.called)
 
     def _check_mount_fstab_subp(self, fdata, expected, target=None):
         # expected currently is like: mount <device> <mp>