validate master option for 'statuslog' and 'statusgui' commands

For 'buildbot statuslog' and 'buildbot statusgui' subcommands, validate
master (-m, --master) option. If not valid print user friendly
error message "master must have the form 'hostname:port'".
validate master option for 'buildbot debugclient' command

If master (-m, --master) option is not valid, print user friendly
error message "master must have the form 'hostname:port'".