More cgptlib tests

Add some extra cases to SanityCheckTest() to test both header and entries
being garbled at either end of the disk.

Add DuplicateUniqueGuidTest() to check that GPTs having duplicate
UniqueGuids in the entries are rejected. We can only check this per-disk, of

Made some changes to the library to enforce the UniqueGuid requirement that
I just started testing for.


Review URL:

Change-Id: I86458faf9cc99aa3f29aac0d5b144dbd05067181
3 files changed