Allow reusing of previous brancher instance

[AlexanderGrooff]

Useful for doing rapid development, and you don't care too much about pristine environments. Instead of creating a new Brancher node when using addBrancherServer, just reuse the last one if there is any.

Note the new --reuse-brancher flag:

$ hypernode-deploy deploy -h
Description:
  Deploy application.

Usage:
  deploy [options] [--] <stage>

Arguments:
  stage                 Stage deploy to

Options:
      --reuse-brancher  Reuse the brancher Hypernode from the previous deploy
  -h, --help            Display help for the given command. When no command is given display help for the list command
  -q, --quiet           Do not output any message
  -V, --version         Display this application version
      --ansi|--no-ansi  Force (or disable --no-ansi) ANSI output
  -n, --no-interaction  Do not ask any interactive question
  -f, --file[=FILE]     Specify configuration file [default: "deploy.php"]
  -v|vv|vvv, --verbose  Increase the verbosity of messages: 1 for normal output, 2 for more verbose output and 3 for debug

[tdgroot]

Very nice! :)