Merge remote-tracking branch 'remotes/dgilbert/tags/pull-migration-20210407b' into...

Merge remote-tracking branch 'remotes/dgilbert/tags/pull-migration-20210407b' into staging

V2 migration+virtiofs fixes pull 2021-04-07

A seg fix in virtiofsd, a bunch of fixes for background snapshots, and
a migration test fix.

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
v2
  Fix for !linux build

# gpg: Signature made Wed 07 Apr 2021 18:53:13 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-20210407b:
  tests/migration: fix parameter of auto-converge migration
  migration: Rename 'bs' to 'block' in background snapshot code
  migration: Pre-fault memory before starting background snasphot
  migration: Inhibit virtio-balloon for the duration of background snapshot
  migration: Fix missing qemu_fflush() on buffer file in bg_migration_thread
  virtiofsd: Fix security.capability comparison

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