additional BTRFS functionality for kickstart

[Gene Czarcinski]

I am attemptint to introduce some new kickstart functionality for BTRFS 
and I have described in my previous emails.

One aspect of this is to support adding existing BTRFS subvolumes to 
/etc/fstab ... just add them, nothing else.

A second aspect to support recreating an existing BTRFS subvolume. That 
is, deleting (destroying) the subvolume and then recreating it with the 
same name.

Both of these capabilities currently exist if you are doing a 
non-kickstart GUI install (probably a text install too but I have not 
tested that).

Yes, I consider that the second "aspect" is the BTRFS "equivalent" of 
reformatting since it has the effect of reclaiming the spece previously 
used by that subvolume and then using that same subvolume name.  I do 
not see this as a big deal.

Currently, for logical volumes, --noformat is used to specify that a 
logical volume should just be mounted and --useexisting is used to 
specify that a logical volume should be reformatted (and mounted) before 
being used.

While I am not oppose to adding new options to the btrfs command, I 
thought that using more or less  the same meaning as for logical 
volumnes made some sense:  --noformat: just mount and add to /etc/fstab; 
--useexisting: destroy and recreate the subvolume.

If it would make everyone happy, I could live with having a new 
--recreate option.

David Lehman and I have been having a spirited discussion about this on 
bugzilla:
https://bugzilla.redhat.com/show_bug.cgi?id=892747
https://bugzilla.redhat.com/show_bug.cgi?id=1019510

I thought it might make sense to see what others might think about it.

Gene