Keep SSH connection open to speed up commands

[westonruter]

Since vassh has to invoke vagrant ssh anew each time it runs, there is the additional overhead of establishing the SSH connection that can take an additional ~1s. If, however, the first time that vaash is invoked we could somehow keep the connection open in the background and then keep re-using it, then it would speed up requests.

See original comment.

[bfintal]

+1

[shkm]

+1 this would be amazing.

[westonruter]

See also: https://github.com/xwp/wp-cli-ssh/issues/15