collect system_info -x fails silently when coordinator node is specified

[mattsfuller]

Instead, it should display a message along the lines of "You can't exclude the node on which presto-admin is installed when running this command"
See a sample run below:
[root@ip-172-30-1-57 ~]# ./prestoadmin/presto-admin collect system_info -x 172.30.1.57
[root@ip-172-30-1-57 ~]#
Also add a positive test for 'collect system_info -x [coordinator name],[worker name]'