Merge remote-tracking branch 'remotes/kevin/tags/for-upstream' into staging

Block layer patches for 2.11.0-rc4

# gpg: Signature made Mon 04 Dec 2017 16:46:07 GMT
# gpg:                using RSA key 0x7F09B272C88F2FD6
# gpg: Good signature from "Kevin Wolf <[email protected]>"
# Primary key fingerprint: DC3D EB15 9A9A F95D 3D74  56FE 7F09 B272 C88F 2FD6

* remotes/kevin/tags/for-upstream:
  blockjob: Make block_job_pause_all() keep a reference to the jobs

Signed-off-by: Peter Maydell <[email protected]>