Check that there is no exclusive backup taking place while we perform

a switchover.

We've found that this can cause some issues with postgres control
metadata (could be a postgres bug) so best thing is *not* no switchover
if there's a backup taking place.

It's also a bad idea from an architectual point of view, as a switchover
is supposed to be planed, so why perform it when we are taking backups.

GitHub #476.

dbutils.c

@@ -3953,7 +3953,31 @@ connection_ping(PGconn *conn)
 	return;
 }
 
+/*
+ * Function that checks if the primary is in exclusive backup mode.
+ * We'll use this when executing an action can conflict with an exclusive
+ * backup.
+ */
+bool
+server_not_in_exclusive_backup_mode(PGconn *conn)
+{
+	PGresult   *res = PQexec(conn, "SELECT pg_is_in_backup()");
 
+	if (PQresultStatus(res) != PGRES_TUPLES_OK)
+	{
+		log_error(_("unable to retrieve information regarding backup mode of node"));
+		log_detail("%s", PQerrorMessage(conn));
+		PQclear(res);
+		return false;
+	}
+
+	if (strcmp(PQgetvalue(res, 0, 0), "t") == 0)
+	{
+		log_warning(_("node is in exclusive backup mode"));
+		return false;
+	}
+	return true;
+}
 
 /* ==================== */
 /* monitoring functions */