[SSH] Add config to speed up connecitons.

* link: http://interrobeng.com/2013/08/25/speed-up-git-5x-to-50x/

Info about the configuration extracted from the post:

* `ControlMaster auto` enables the sharing of multiple SSH sessions
  over a single network connection, and auto-creating a master
  connection if it does not already exist.
* `ControlPath /tmp/%r@%h:%p` specifies the path to the control socket
  used for connection sharing. %r will be substituted by the remote
  login username, %h by the target host name and %p by the port.
* `ControlPersist yes` keeps the master connection open in the
  background indefinitely.