Reverting partition's size shouldn't require it to be aligned (#1165714)

If the original size was unaligned, it's not our fault and we can do nothing
about it.
Try to get FS info first before doing an FS check

Running an FS check implicitly may slow things down quite a big and may result
in changes users didn't expect to happen while probing their file systems.

Related: rhbz#1162215
Prune actions before cancelling them

If we were to process the actions, we would prune them first because some
actions just annihilate with some others. We can do the same before cancelling
scheduled actions which may save us from cancelling actions that would be
eliminated by cancelling other actions. This speeds things up and save us from
doing many potentially dangerous things caused by cancelling actions.

Related: rhbz#1165714
Related: rhbz#1166598