Exclude holes from the block map.

e2fsdroid can export holes as a "0" block, in order to make sure logical
and physical block assignments are maintained properly. Exclude these
hole blocks from range sets in LoadFileBlockMap.

Bug: 139201772
Test: m dist on non-A/B
Change-Id: Ic04e869572229678fdeaaa6fbf6f464d6c672051