Fix ephemeral mounts

Add all possible ephemeral block mounts during AMI registration

Value for this being if not using directly AWS to launch a server (ergo skipping the assignment).

Prime case is Rightscale: they create their images with 1-4 ephemeral mounts. Due to this on some instance sizes you don't see all the available ephemeral storage and there is no way to add it afterwards.
Good one, thanks

As for the missind devices:
 * sda - root device
 * sdz - snot used as the max number of ephemerals supported by aws is 24