Arthur/ssh check

Check meant to:
1. Check the status of SFTP
2.Check The response time 


@LeoCavaille 
ssh_check could be a generic check for SSH and optional SFTP. You always test the SSH connection, so it's a close to zero overhead to add a service check for SSH.

![](http://bbsimg.ngfiles.com/15/25162000/ngbbs53ca82cd9d79a.jpg)