Improve docker-related query test failure avoidance

src/pgmon.py

@@ -656,15 +656,24 @@ def test_queries():
         # If the metric has arguments to use while testing, grab those
         args = metric.get("test_args", {})
         print("Testing {} [{}]".format(name, ", ".join(["{}={}".format(key, value) for key, value in args.items()])))
-        # Run the query with the ability to retry, mostly because the PostgreSQL
-        # docker image restarts during its initialization phase.  If the health
-        # check passes during the first phase, the agent will start testing too
-        # early and will break when PostgreSQL restarts.
-        try:
-            res = sample_metric(dbname, name, args, retry=True)
-        except MetricVersionError:
-            print("{} -> Unsupported for this version".format(name))
-            continue
+        # When testing against a docker container, we may end up connecting
+        # before the service is truly up (it restarts during the initialization
+        # phase).  To cope with this, we'll allow a few connection failures.
+        tries = 5
+        while True:
+            # Run the query without the ability to retry
+            try:
+                res = sample_metric(dbname, name, args, retry=False)
+                break
+            except MetricVersionError:
+                res = "Unsupported for this version"
+                break
+            except psycopg2.OperationalError as e:
+                print("Error encountered, {} tries left: {}".format(tries, e))
+                if tries <= 0:
+                    raise
+                time.sleep(1)
+            tries -= 1
         # Compare the result to the provided sample results
         # TODO
         print("{} -> {}".format(name, res))