tests: fixes for issues uncovered when moving to python 3.6.

This includes a few fixes found when testing with python 3.6.
 - fix eni renderer when target is None
   This just uses the util.target_path() in the event that target is None.
 - change test cases to not rely on the cached result of
   util.get_cmdline() and other cached globals. Update the base TestCase
   to unset that cache.
 - mock calls to system_is_snappy from the create_users test cases.
 - drop unused _pp_root in test_simple_run.py

LP: #1703697

1 files changed, 20 insertions, 1 deletions

diff --git a/tests/unittests/helpers.py b/tests/unittests/helpers.py
index 569f1aef..6691cf82 100644
--- a/tests/unittests/helpers.py
+++ b/tests/unittests/helpers.py
@@ -82,7 +82,26 @@ def retarget_many_wrapper(new_base, am, old_func):
 
 
 class TestCase(unittest2.TestCase):
-    pass
+    def reset_global_state(self):
+        """Reset any global state to its original settings.
+
+        cloudinit caches some values in cloudinit.util.  Unit tests that
+        involved those cached paths were then subject to failure if the order
+        of invocation changed (LP: #1703697).
+
+        This function resets any of these global state variables to their
+        initial state.
+
+        In the future this should really be done with some registry that
+        can then be cleaned in a more obvious way.
+        """
+        util.PROC_CMDLINE = None
+        util._DNS_REDIRECT_IP = None
+        util._LSB_RELEASE = {}
+
+    def setUp(self):
+        super(unittest2.TestCase, self).setUp()
+        self.reset_global_state()
 
 
 class CiTestCase(TestCase):