test: added tests for https-agent-getname

PR-URL: https://github.com/nodejs/node/pull/6762


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Brian White <mscdex@mscdex.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Fedor Indutny <fedor.indutny@gmail.com>
Reviewed-By: Johan Bergström <bugs@bergstroem.nu>