Add support to username login.

Allow to specify an username to login when interacting with Autotest Server.
Fix issue #6.

Signed-off-by: Ruda Moura <rmoura@redhat.com>
Parse argument option --username.

Fix issue #6.

Signed-off-by: Ruda Moura <rmoura@redhat.com>
Merge pull request #7 from ruda/username_login

Code looks great and works as advertised!

Thanks!