Merge ~xavpaice/charm-nagios:lp1712977 into ~nagios-charmers/charm-nagios:master

[Xav Paice]

[James Hebden (ec0)]

LGTM

review: Approve

diff --git a/hooks/charmhelpers/core/hookenv.py b/hooks/charmhelpers/core/hookenv.py
index 12f37b2..899722f 100644
--- a/hooks/charmhelpers/core/hookenv.py
+++ b/hooks/charmhelpers/core/hookenv.py
@@ -218,6 +218,8 @@ def principal_unit():
         for rid in relation_ids(reltype):
             for unit in related_units(rid):
                 md = _metadata_unit(unit)
+                if not md:
+                    continue
                 subordinate = md.pop('subordinate', None)
                 if not subordinate:
                     return unit
@@ -511,7 +513,10 @@ def _metadata_unit(unit):
     """
     basedir = os.sep.join(charm_dir().split(os.sep)[:-2])
     unitdir = 'unit-{}'.format(unit.replace(os.sep, '-'))
-    with open(os.path.join(basedir, unitdir, 'charm', 'metadata.yaml')) as md:
+    joineddir = os.path.join(basedir, unitdir, 'charm', 'metadata.yaml')
+    if not os.path.exists(joineddir):
+        return None
+    with open(joineddir) as md:
         return yaml.safe_load(md)