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
I suppose the question here is: "is EBS being available considered a pre-requisite for our system being stable", I'm under the impression that it is (hence this arc of work), and as a result believe these should not be forced to act as though they worked when they did not.

If a system could benefit from EBS, but does not require it, then they could `|| true` this line as you rightly point out.