[etcd] send service check ok when all is fine

And not only CRITICAL when unable to get metrics.
This is needed as the service check won't appear on the monitor screen
otherwise.
Fix python2.6 compatibility issue: "{}".format()

checks.d/etcd.py

@@ -54,7 +54,7 @@ def check(self, instance):
         instance_tags = instance.get('tags', [])
         # Append the instance's URL in case there are more than one, that
         # way they can tell the difference!
-        instance_tags.append("url:{}".format(url))
+        instance_tags.append("url:{0}".format(url))
         timeout = float(instance.get('timeout', self.DEFAULT_TIMEOUT))
 
         self_response = self.get_self_metrics(url, timeout)
@@ -68,27 +68,30 @@ def check(self, instance):
                 if key in self_response:
                     self.rate(self.SELF_RATES[key], self_response[key], tags=instance_tags)
                 else:
-                    self.log.warn("Missing key {} in stats.".format(key))
+                    self.log.warn("Missing key {0} in stats.".format(key))
 
             for key in self.SELF_GAUGES:
                 if key in self_response:
                     self.gauge(self.SELF_GAUGES[key], self_response[key], tags=instance_tags)
                 else:
-                    self.log.warn("Missing key {} in stats.".format(key))
+                    self.log.warn("Missing key {0} in stats.".format(key))
 
         store_response = self.get_store_metrics(url, timeout)
         if store_response is not None:
             for key in self.STORE_RATES:
                 if key in store_response:
                     self.rate(self.STORE_RATES[key], store_response[key], tags=instance_tags)
                 else:
-                    self.log.warn("Missing key {} in stats.".format(key))
+                    self.log.warn("Missing key {0} in stats.".format(key))
 
             for key in self.STORE_GAUGES:
                 if key in store_response:
                     self.gauge(self.STORE_GAUGES[key], store_response[key], tags=instance_tags)
                 else:
-                    self.log.warn("Missing key {} in stats.".format(key))
+                    self.log.warn("Missing key {0} in stats.".format(key))
+
+        if self_response is not None and store_response is not None:
+            self.service_check(self.SERVICE_CHECK_NAME, AgentCheck.OK, tags=instance_tags)
 
     def get_self_metrics(self, url, timeout):
         return self.get_json(url + "/v2/stats/self", timeout)
@@ -103,13 +106,13 @@ def get_json(self, url, timeout):
             # If there's a timeout
             self.service_check(self.SERVICE_CHECK_NAME, AgentCheck.CRITICAL,
                 message="Timeout when hitting %s" % url,
-                tags = ["url:{}".format(url)])
-            return None
+                tags = ["url:{0}".format(url)])
+            raise
 
         if r.status_code != 200:
             self.service_check(self.SERVICE_CHECK_NAME, AgentCheck.CRITICAL,
                 message="Got %s when hitting %s" % (r.status_code, url),
-                tags = ["url:{}".format(url)])
-            return None
+                tags = ["url:{0}".format(url)])
+            raise Exception("Http status code {0} on url {1}".format(r.status_code, url))
 
         return r.json()