Merge remote-tracking branch 'remotes/dgilbert/tags/pull-migration-20180926a' into staging

Migration pull 2018-09-26

This supercedes Juan's pull from the 13th

# gpg: Signature made Wed 26 Sep 2018 18:07:30 BST
# gpg:                using RSA key 0516331EBC5BFDE7
# gpg: Good signature from "Dr. David Alan Gilbert (RH2) <dgilbert@redhat.com>"
# Primary key fingerprint: 45F5 C71B 4A0C B7FB 977A  9FA9 0516 331E BC5B FDE7

* remotes/dgilbert/tags/pull-migration-20180926a:
  migration/ram.c: Avoid taking address of fields in packed MultiFDInit_t struct
  migration: fix the compression code
  migration: fix QEMUFile leak
  tests/migration: Speed up the test on ppc64
  migration: cleanup in error paths in loadvm
  migration/postcopy: Clear have_listen_thread
  tests/migration: Add migration-test header file
  tests/migration: Support cross compilation in generating boot header file
  tests/migration: Convert x86 boot block compilation script into Makefile
  migration: use save_page_use_compression in flush_compressed_data
  migration: show the statistics of compression
  migration: do not flush_compressed_data at the end of iteration
  Add a hint message to loadvm and exits on failure
  migration: handle the error condition properly
  migration: fix calculating xbzrle_counters.cache_miss_rate
  migration/rdma: Fix uninitialised rdma_return_path

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