Xd 2145 - Authenticated shell support (apply after 1201)

Shell changes: …
* Use Apache HttpClient for authentication in the Shell
* admin config server' now supports the '--username' and '--password' parameters
* Supporting unit tests for HTTPS and authentication in the Shell
@ilayaperumalg I would like to keep them in, though. @markpollack is working on a Spring Shell fix that should address the `--host` and `--port` issues as well, so in the interest of consistency, I'd like to keep credentials, too (even if we know that they do not really work at least we have a complete picture of how the shell launch option is supposed to work - and the credentials are are an integral part of that).