Merge lp:~barryprice/charms/xenial/daisy-retracer/trunk into lp:~daisy-pluckers/charms/xenial/daisy-retracer/trunk

[Barry Price]

Ensure nrpe relation actually has a unit ID before attempting to use it

Seen deploying a couple of new units recently, when RELATION_ID was defined, but a relation-list didn't yet return any units:

+ nrpe_setup
++ relation-ids nrpe-external-master
+ RELATION_ID=nrpe-external-master:193
+ '[' -z nrpe-external-master:193 ']'
++ relation-list -r nrpe-external-master:193
+ relation_unit=
++ relation-get -r nrpe-external-master:193 nagios_host_context
ERROR no unit or application specified
+ nagios_host_context=

=== modified file 'hooks/common'
--- hooks/common	2020-06-09 01:54:06 +0000
+++ hooks/common	2021-03-26 09:45:25 +0000
@@ -310,6 +310,10 @@
         return 0
     fi
     relation_unit=$(relation-list -r $RELATION_ID)
+    if [ -z "$relation_unit" ]; then
+        echo "No nrpe-external-master relation unit yet. Skipping nrpe setup"
+        return 0
+    fi
     nagios_host_context=$(relation-get -r $RELATION_ID nagios_host_context $relation_unit)
     export NAGIOS_HOSTNAME=$(relation-get -r $RELATION_ID nagios_hostname $relation_unit)
     export INSTANCE_TYPE