Make use of /usr/sbin/ebslvm

The new baseami provides /usr/sbin/ebslvm which we use
here to mount ebs volumes in an lvm in /mnt, that means
we no longer provide the symlink during the build phase
causes moutns to happen at instance boot
Merge pull request #5 from TwitchScience/setup_ebslvm

Make use of /usr/sbin/ebslvm