[CHEF-3835] Fix net-ssh* gem dependencies.

http://tickets.opscode.com/browse/CHEF-3835

New versions of net-ssh-multi and net-ssh-gateway depend on `net-ssh >= 2.6.4` which breaks chef's dependency on `net-ssh ~> 2.2.2`.

This locks `net-ssh-multi` and `net-ssh-gateway` at `1.1.0`