Btrfs: free up block groups after everything

Btrfs: free up block groups after everything

If we abort a transaction we will do the tree log cleanup at unmount, but this
happens after we free up the block groups.  This makes all the leak detection
warnings go off because we think we've leaked space but in reality we just
haven't cleaned it up yet.  So instead do the block group cleanup stuff after
free'ing the fs roots so we don't get these warnings.  Thanks,

Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>