Have the distro automatically populate a name from the filename

Make it so that the previous setting of 'rhel' for a persona worked
and that it automatically works in the future when new distros are
added the distro name (which is verified when loading the persona
is sucked up from the distro filename when it is not present).

Change-Id: I15c2dfda2673b7e2f89e5cb6a0bc2691511f1a0b
Merge "Have the distro automatically populate a name from the filename"