Add an OpenSSH module

This is basic ssh functions and a higher level function for require.ssh.
Import git module into the require module namespace
remove ssh from the require module
More robust implementations of the disable_* functions and added the
enable_* functions.

The harden() function is now in the fabtools.ssh module. sshd_config
file is now a parameter. ssh is restarted after any of these
functions.
Merge pull request #104 from adamrt/ssh-module

Add ssh module for hardening OpenSSH