Service#enable and #disable should use Sysvinit chkconfig/service on rhel 6.4

[jrafanie]

It appears rhel 6.4 still uses Sysvinit so, the calls to systemctl fail:

irb(main):010:0> service.disable
Errno::ENOENT: No such file or directory - /bin/systemctl disable xyz.service

http://fedoraproject.org/wiki/SysVinit_to_Systemd_Cheatsheet
http://sys-log.tumblr.com/post/16117093002/cheat-sheet-chkconfig-vs-systemctl

[jrafanie]

@movitto Can you take a look at this one?

[movitto]

@jrafanie see pull request #50

[jrafanie]

Fixed by #50