In archive_write_disk: If archive_write_header() fails to create
the file, that's a failure and should return ARCHIVE_FAILED.
Metadata restore failures still return ARCHIVE_WARN, because
that's non-critical. Fix test_write_disk_secure test to
verify the correct return code in one case; add test_write_disk_failures
to do another very simple test of restore failure.
This should fix cpio coredumping when it tries to restore to
a write-protected directory.
Thanks to: Giorgos Keramidas
MFC after: 30 days
53272655f6