Ensure get_requests_for_local_unit doesn't fail on incomplete relation

This is a rebuild/make sync for charms to pickup the fix in charmhelpers to fix
any inadvertant accesses of ['ca'] in the relation data before it is available
from vault in the certificates relation.  Fix in charmhelpers is in [1].

[1] https://github.com/juju/charm-helpers/pull/824
Closes-Bug: #2028683

Change-Id: Ie05a9ff536700282dc0c66816b50efee5da62767

hooks/charmhelpers/core/unitdata.py

@@ -529,7 +529,8 @@ def kv():
 
     env_var = os.environ.get("CHARM_HELPERS_TESTMODE", "auto").lower()
     if env_var not in ["auto", "no", "yes"]:
-        logging.warning(f"Unknown value for CHARM_HELPERS_TESTMODE '{env_var}', assuming 'no'")
+        logging.warning("Unknown value for CHARM_HELPERS_TESTMODE '%s'"
+                        ", assuming 'no'", env_var)
         env_var = "no"
 
     if env_var == "no":

hooks/charmhelpers/fetch/snap.py

@@ -52,7 +52,7 @@ def _snap_exec(commands):
     :param commands: List commands
     :return: Integer exit code
     """
-    assert type(commands) == list
+    assert isinstance(commands, list)
 
     retry_count = 0
     return_code = None