Merge remote-tracking branch 'remotes/elmarco/tags/dump-pull-request' into staging

Pull request

# gpg: Signature made Wed 21 Mar 2018 14:37:05 GMT
# gpg:                using RSA key DAE8E10975969CE5
# gpg: Good signature from "Marc-André Lureau <marcandre.lureau@redhat.com>"
# gpg:                 aka "Marc-André Lureau <marcandre.lureau@gmail.com>"
# Primary key fingerprint: 87A9 BD93 3F87 C606 D276  F62D DAE8 E109 7596 9CE5

* remotes/elmarco/tags/dump-pull-request:
  dump-guest-memory: more descriptive lookup_type failure
  dump.c: allow fd_write_vmcore to return errno on failure

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>