tests: Disallow use of util.subp except for where needed.

In many cases, cloud-init uses 'util.subp' to run a subprocess.
This is not really desirable in our unit tests as it makes the tests
dependent upon existance of those utilities.

The change here is to modify the base test case class (CiTestCase) to
raise exception any time subp is called.  Then, fix all callers.
For cases where subp is necessary or actually desired, we can use it
via
  a.) context hander CiTestCase.allow_subp(value)
  b.) class level self.allowed_subp = value

Both cases the value is a list of acceptable executable names that
will be called (essentially argv[0]).

Some cleanups in AltCloud were done as the code was being updated.

1 files changed, 5 insertions, 2 deletions

diff --git a/cloudinit/config/tests/test_snap.py b/cloudinit/config/tests/test_snap.py
index 34c80f1e..3c472891 100644
--- a/cloudinit/config/tests/test_snap.py
+++ b/cloudinit/config/tests/test_snap.py
@@ -162,6 +162,7 @@ class TestAddAssertions(CiTestCase):
 class TestRunCommands(CiTestCase):
 
     with_logs = True
+    allowed_subp = [CiTestCase.SUBP_SHELL_TRUE]
 
     def setUp(self):
         super(TestRunCommands, self).setUp()
@@ -424,8 +425,10 @@ class TestHandle(CiTestCase):
             'snap': {'commands': ['echo "HI" >> %s' % outfile,
                                   'echo "MOM" >> %s' % outfile]}}
         mock_path = 'cloudinit.config.cc_snap.sys.stderr'
-        with mock.patch(mock_path, new_callable=StringIO):
-            handle('snap', cfg=cfg, cloud=None, log=self.logger, args=None)
+        with self.allow_subp([CiTestCase.SUBP_SHELL_TRUE]):
+            with mock.patch(mock_path, new_callable=StringIO):
+                handle('snap', cfg=cfg, cloud=None, log=self.logger, args=None)
+
         self.assertEqual('HI\nMOM\n', util.load_file(outfile))
 
     @mock.patch('cloudinit.config.cc_snap.util.subp')