Remove passwd from test configurations

As the parameter will be removed in 2.3, the test configurations need to
be updated.

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

@@ -6,7 +6,7 @@ type=monitor
 module=mysqlmon
 servers=server1,server2,server3
 user=maxskysql
-passwd=skysql
+password=skysql
 monitor_interval=1000
 detect_standalone_master=true
 failcount=1
@@ -25,7 +25,7 @@ type=service
 router=readwritesplit
 servers=server1,server2,server3
 user=maxskysql
-passwd=skysql
+password=skysql
 
 [RW Split Listener]
 type=listener