MXS-359: Test read-only mode and master replacement

Added test cases that verify that the functionality works as
expected. Also made Mariadb_nodes::change_master less verbose when one of
the nodes is down.

maxscale-system-test/cnf/maxscale.cnf.template.mxs359_read_only

@@ -0,0 +1,60 @@
+[maxscale]
+threads=###threads###
+
+[MySQL-Monitor]
+type=monitor
+module=mysqlmon
+###repl51###
+servers=server1,server2,server3,server4
+user=maxskysql
+passwd=skysql
+monitor_interval=1000
+
+[RW-Split-Router]
+type=service
+router=readwritesplit
+servers=server1,server2,server3,server4
+user=maxskysql
+passwd=skysql
+allow_master_change=true
+master_failure_mode=fail_on_write
+
+[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
+
+[server4]
+type=server
+address=###node_server_IP_4###
+port=###node_server_port_4###
+protocol=MySQLBackend