Merge remote-tracking branch 'remotes/dgilbert/tags/pull-migration-20200703a' into staging

virtiofsd+migration pull 2020-07-03

A couple of small migration fixes, and some capability
rework for virtiofsd.

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

# gpg: Signature made Fri 03 Jul 2020 16:26:35 BST
# gpg:                using RSA key 45F5C71B4A0CB7FB977A9FA90516331EBC5BFDE7
# gpg: Good signature from "Dr. David Alan Gilbert (RH2) <dgilbert@redhat.com>" [full]
# Primary key fingerprint: 45F5 C71B 4A0C B7FB 977A  9FA9 0516 331E BC5B FDE7

* remotes/dgilbert/tags/pull-migration-20200703a:
  migration: Count new_dirty instead of real_dirty
  migration: postcopy take proper error return
  virtiofsd: Allow addition or removal of capabilities
  virtiofsd: Check capability calls
  virtiofsd: Terminate capability list

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