Allow retry in query tests

src/pgmon.py

@@ -656,9 +656,12 @@ 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 without the ability to retry.
+        # 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=False)
+            res = sample_metric(dbname, name, args, retry=True)
         except MetricVersionError:
             print("{} -> Unsupported for this version".format(name))
             continue