block/dmg: process a buffer instead of reading ints

block/dmg: process a buffer instead of reading ints

As the decoded plist XML is not a pointer in the file,
dmg_read_mish_block must be able to process a buffer instead of a file
pointer. Since the full buffer must be processed, let's change the
return value again to just a success flag.

Signed-off-by: Peter Wu <peter@lekensteyn.nl>
Reviewed-by: John Snow <jsnow@redhat.com>
Message-id: 1420566495-13284-5-git-send-email-peter@lekensteyn.nl
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>