Fix /var unmounting bug

When a root partition has a separate /var partition, that /var
partition is mounted, added to the activated list, then unmounted.
The problem is that it is never removed from the activated list, thus
when all partitions are unmounted later on, an error occurs as YaST
tries to unmount it twice.
Merge pull request #3 from jgiannuzzi/var_unmounting_bug

Fix /var unmounting bug