Merge remote-tracking branch 'remotes/dgilbert/tags/pull-migration-20200313a' into...

Migration pull 2020-03-13

zstd build fix
A new auto-converge parameter
Some COLO improvements

# gpg: Signature made Fri 13 Mar 2020 10:29:34 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/tags/pull-migration-20200313a:
  migration: recognize COLO as part of activating process
  ram/colo: only record bitmap of dirty pages in COLO stage
  COLO: Optimize memory back-up process
  migration/throttle: Add throttle-trig-thres migration parameter
  configure: Improve zstd test

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