Add test case for ignore_external_masters + failover

The test checks that failover works even when the master of the monitored
cluster is a slave to an external masters. The test also verifies that the
servers do not get unexpected status labels.

maxscale-system-test/cnf/maxscale.cnf.template.mysqlmon_external_master

@@ -0,0 +1,59 @@
+[maxscale]
+threads=###threads###
+
+[MySQL-Monitor]
+type=monitor
+module=mysqlmon
+servers=server1,server2,server3
+user=maxskysql
+passwd=skysql
+monitor_interval=1000
+detect_standalone_master=true
+failcount=1
+allow_cluster_recovery=true
+auto_failover=true
+auto_rejoin=true
+replication_user=repl
+replication_password=repl
+ignore_external_masters=true
+
+[RW Split Router]
+type=service
+router=readwritesplit
+servers=server1,server2,server3
+user=maxskysql
+passwd=skysql
+
+[RW Split Listener]
+type=listener
+service=RW Split Router
+protocol=MySQLClient
+port=4006
+
+[CLI]
+type=service
+router=cli
+
+[CLI Listener]
+type=listener
+service=CLI
+protocol=maxscaled
+socket=default
+
+[server1]
+type=server
+address=###node_server_IP_1###
+port=###node_server_port_1###
+protocol=MySQLBackend
+
+[server2]
+type=server
+address=###node_server_IP_2###
+port=###node_server_port_2###
+protocol=MySQLBackend
+
+[server3]
+type=server
+address=###node_server_IP_3###
+port=###node_server_port_3###
+protocol=MySQLBackend