Use RFC3339 format for timestamps in SQL module (elastic#15847)

This way timezone and more precise information is stored in the final
events in case they are lately parsed as dates.

CHANGELOG.next.asciidoc

@@ -63,6 +63,8 @@ https://github.com/elastic/beats/compare/v7.0.0-alpha2...master[Check the HEAD d
 
 *Metricbeat*
 
+- Use RFC3339 format for timestamps collected using the SQL module. {pull}15847[15847]
+
 
 *Packetbeat*
 

x-pack/metricbeat/module/sql/query/_meta/data_postgres.json

@@ -10,7 +10,7 @@
         "period": 10000
     },
     "service": {
-        "address": "172.22.0.2:5432",
+        "address": "192.168.0.3:5432",
         "type": "sql"
     },
     "sql": {
@@ -19,27 +19,27 @@
             "numeric": {
                 "blk_read_time": 0,
                 "blk_write_time": 0,
-                "blks_hit": 1923,
-                "blks_read": 111,
+                "blks_hit": 948,
+                "blks_read": 96,
                 "conflicts": 0,
                 "datid": 12379,
                 "deadlocks": 0,
                 "numbackends": 1,
                 "temp_bytes": 0,
                 "temp_files": 0,
                 "tup_deleted": 0,
-                "tup_fetched": 1249,
+                "tup_fetched": 616,
                 "tup_inserted": 0,
-                "tup_returned": 1356,
+                "tup_returned": 717,
                 "tup_updated": 0,
-                "xact_commit": 18,
+                "xact_commit": 3,
                 "xact_rollback": 0
             },
             "string": {
                 "datname": "postgres",
-                "stats_reset": "2020-01-21 11:23:56.53"
+                "stats_reset": "2020-01-25T18:21:44.869405Z"
             }
         },
-        "query": "select * from pg_stat_database"
+        "query": "select * from pg_stat_database where datname='postgres'"
     }
 }

x-pack/metricbeat/module/sql/query/query.go

@@ -150,7 +150,7 @@ func getValue(pval *interface{}) string {
 	case []byte:
 		return string(v)
 	case time.Time:
-		return v.Format("2006-01-02 15:04:05.999")
+		return v.Format(time.RFC3339Nano)
 	default:
 		return fmt.Sprint(v)
 	}

x-pack/metricbeat/module/sql/query/query_integration_test.go

@@ -73,7 +73,7 @@ func TestPostgreSQL(t *testing.T) {
 
 	config = testFetchConfig{
 		Driver:    "postgres",
-		Query:     "select * from pg_stat_database",
+		Query:     "select * from pg_stat_database where datname='postgres'",
 		Host:      fmt.Sprintf("postgres://%s:%s@%s:%s/?sslmode=disable", user, password, host, port),
 		Assertion: assertFieldNotContains("service.address", ":"+password+"@"),
 	}