tools/testing/selftests: test MREMAP_DONTUNMAP on multiple VMA move

tools/testing/selftests: test MREMAP_DONTUNMAP on multiple VMA move

We support MREMAP_MAYMOVE | MREMAP_FIXED | MREMAP_DONTUNMAP for moving
multiple VMAs via mremap(), so assert that the tests pass with both
MREMAP_DONTUNMAP set and not set.

Additionally, add success = false settings when mremap() fails.  This is
something that cannot realistically happen, so in no way impacted test
outcome, but it is incorrect to indicate a test pass when something has
failed.

Link: https://lkml.kernel.org/r/d7359941981e4e44c774753b3e364d1c54928e6a.1753119043.git.lorenzo.stoakes@oracle.com
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Jann Horn <jannh@google.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>