setup: add support my unix_socket authenticated mysql server

Summary:
This patch adds support support for unix_socket based authentication against
mariadb servers. Unix_socket support was also edit to the setup dial when
calling setup-kolab (roundcube|syncrotron|mysql)

Test Plan: Use --mysqlserver=unix_socket or --mysqlserver=existing --mysqlrootpw=unix_socket.

Reviewers: PyKolab Developers, vanmeeuwen

Reviewed By: PyKolab Developers, vanmeeuwen

Subscribers: vanmeeuwen

Differential Revision: https://git.kolab.org/D865