Fix Nagios additional checks functionality

Commit 40b22e3d on juju/charm-helpers repo introduced shell quoting of
each argument passed to the check, turning the quoting of the double quotes
done here not only unnecessary but also damaging to the final command.

Closes-Bug: #2008784
Change-Id: Ifedd5875d27e72a857b01a48afcd058476734695
func-test-pr: https://github.com/openstack-charmers/zaza-openstack-tests/pull/1022

src/ceph_hooks.py

@@ -1167,7 +1167,7 @@ def update_nrpe_config():
             name = "ceph-{}".format(key.replace(" ", ""))
             log("Adding check {}".format(name))
             check_cmd = 'check_ceph_status.py -f {}' \
-                ' --additional_check \\\"{}\\\"' \
+                ' --additional_check \"{}\"' \
                 ' {}'.format(STATUS_FILE, value,
                              "--additional_check_critical"
                              if additional_critical is True else "")