"repmgr bdr register": create missing connection replication set if needed

Previously the assumption was that the "repmgr" replication set would be
set up when the nodes are created, however no checks were implemented
and this was not well-documented.

Addresses GitHub #347.

dbutils.c

@@ -4596,3 +4596,71 @@ unset_bdr_failover_handler(PGconn *conn)
 	PQclear(res);
 	return;
 }
+
+
+bool
+bdr_node_has_repmgr_set(PGconn *conn, const char *node_name)
+{
+	PQExpBufferData query;
+	PGresult   *res = NULL;
+	bool		has_repmgr_set = false;
+
+	initPQExpBuffer(&query);
+
+	appendPQExpBuffer(&query,
+					  " SELECT COUNT(*) "
+					  "   FROM UNNEST(bdr.connection_get_replication_sets('%s') AS repset "
+					  "  WHERE repset = 'repmgr'",
+					  node_name);
+
+	res = PQexec(conn, query.data);
+	termPQExpBuffer(&query);
+
+	if (PQresultStatus(res) != PGRES_TUPLES_OK || PQntuples(res) == 0)
+	{
+		has_repmgr_set = false;
+	}
+	else
+	{
+		has_repmgr_set = atoi(PQgetvalue(res, 0, 0)) == 1 ? true : false;
+	}
+
+	PQclear(res);
+
+	return has_repmgr_set;
+}
+
+
+bool
+bdr_node_set_repmgr_set(PGconn *conn, const char *node_name)
+{
+	PQExpBufferData query;
+	PGresult   *res = NULL;
+	bool		success = true;
+
+	initPQExpBuffer(&query);
+
+	appendPQExpBuffer(&query,
+					  " SELECT bdr.connection_set_replication_sets( "
+					  "   ARRAY( "
+					  "     SELECT repset::TEXT "
+					  "       FROM UNNEST(bdr.connection_get_replication_sets('node1')) AS repset "
+					  "         UNION "
+					  "     SELECT 'repmgr'::TEXT "
+					  "   ), "
+					  "   '%s' "
+					  " ) ",
+					  node_name);
+
+	res = PQexec(conn, query.data);
+	termPQExpBuffer(&query);
+
+	if (PQresultStatus(res) != PGRES_TUPLES_OK)
+	{
+		success = false;
+	}
+
+	PQclear(res);
+
+	return success;
+}