Support charms without pause/resume actions

Change-Id: Idc3435743105af3e4d702e73d59d7b141afd2d26

ops_openstack/core.py

@@ -72,8 +72,20 @@ class OSBaseCharm(CharmBase):
         self._stored.set_default(series_upgrade=False)
         self.framework.observe(self.on.install, self.on_install)
         self.framework.observe(self.on.update_status, self.on_update_status)
-        self.framework.observe(self.on.pause_action, self.on_pause_action)
-        self.framework.observe(self.on.resume_action, self.on_resume_action)
+        # A charm may not have pause/resume actions if it does not manage a
+        # daemon.
+        try:
+            self.framework.observe(
+                self.on.pause_action,
+                self.on_pause_action)
+        except AttributeError:
+            pass
+        try:
+            self.framework.observe(
+                self.on.resume_action,
+                self.on_resume_action)
+        except AttributeError:
+            pass
         self.framework.observe(self.on.pre_series_upgrade,
                                self.on_pre_series_upgrade)
         self.framework.observe(self.on.post_series_upgrade,