Merge remote-tracking branch 'remotes/dgilbert-gitlab/tags/pull-virtiofs-20210216' into staging

virtiofsd pull 2021-02-16

Vivek's support for new FUSE KILLPRIV_V2
and some smaller cleanups.

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

# gpg: Signature made Tue 16 Feb 2021 18:34:32 GMT
# 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-gitlab/tags/pull-virtiofs-20210216:
  virtiofsd: Do not use a thread pool by default
  viriofsd: Add support for FUSE_HANDLE_KILLPRIV_V2
  virtiofsd: Save error code early at the failure callsite
  tools/virtiofsd: Replace the word 'whitelist'
  virtiofsd: vu_dispatch locking should never fail
  virtiofsd: Allow to build it without the tools

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