Support ssh keys for git operations

[bcremer]

This can be archived using an ENV var.

http://alvinabad.wordpress.com/2013/03/23/how-to-specify-an-ssh-key-file-with-the-git-command/

[bcremer]

We might need a little ssh wrapper script for that:
bin/ssh-as.sh

#!/bin/bash
set -e
set -u

ssh -i $SSH_KEYFILE $@

Also the ssh-key and the wrapper script must be available in the filesystem, so the files must be copied from the phar into the config dir/runtime dir:

$commandline = 'git ' . $commandline;

$env = array(
    'SSH_KEYFILE' => '~/.config/sw-cli-tools/stash_read_only_key.txt',
    'GIT_SSH'     => '/run/user/1000/sw-cli-tools/sw-cli-tools/bin/ssh-as.sh'
);

$process = new Process($commandline, null, $env);
$process->setTimeout(self::DEFAULT_TIMEOUT);

[bcremer]

This has been fixed with: fbfe65f