[Fedora-spins] Fixing the f21 branch of spin-kickstarts

[Bruno Wolff III]

I reverted to back before Luya's errant merge.

Matthew removed the cloud big data spin after the errant merge, but I 
think that was only necessary because of the errant merge. It is gone 
now.

Matthew's other commit (dd extlinux mbr during post as temporary workaround 
for bug #1147998) is not applying cleanly and needs to be looked at.

Luya needs to correctly do whatever he was trying to do originally.

In theory we are in a freeze now, so these changes should only be done now 
if they are needed for freeze exception or blocker for beta. Otherwise 
wait until after beta is gold.