Install python3-croniter for nrpe checks

Change ab79c3ee introduced the croniter library for interacting
with cron. However, the dependent package was not included in
a list of installation packages nor installed on the upgrade
path. This patch adds the python3-croniter package for upgrade
and installation paths to allow the nrpe checks to continue
to function.

Change-Id: I363f8e04a3850eecf219c5a26ab9137f217a0f36
Closes-Bug: #1928802

hooks/rabbit_utils.py

@@ -93,7 +93,8 @@ from charmhelpers.fetch import (
 from charmhelpers.fetch import get_upstream_version
 
 
-PACKAGES = ['rabbitmq-server', 'python3-amqplib', 'lockfile-progs']
+PACKAGES = ['rabbitmq-server', 'python3-amqplib', 'lockfile-progs',
+            'python3-croniter']
 
 VERSION_PACKAGE = 'rabbitmq-server'
 

hooks/rabbitmq_server_relations.py

@@ -641,9 +641,13 @@ def upgrade_charm():
     # for the check_rabbitmq.py script, python3-amqplib needs to be installed;
     # if previous version was a python2 version of the charm this won't happen
     # unless the source is changed.  Ensure it is installed here if needed.
+    # LP:#1928802 - also include python3-croniter as its needed for
+    # check_rabbitmq_queues.py as of change ab79c3ee
     apt_update(fatal=True)
-    if filter_installed_packages(['python3-amqplib']):
-        apt_install(['python3-amqplib'], fatal=True)
+    missing_packages = filter_installed_packages(['python3-amqplib',
+                                                  'python3-croniter'])
+    if missing_packages:
+        apt_install(missing_packages, fatal=True)
 
 
 MAN_PLUGIN = 'rabbitmq_management'