Merge remote-tracking branch 'remotes/dgilbert/tags/pull-hmp-20171214' into staging

HMP pull 2017-12-14

# gpg: Signature made Thu 14 Dec 2017 12:46:41 GMT
# gpg:                using RSA key 0x0516331EBC5BFDE7
# 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-hmp-20171214:
  tests: test-hmp: print command execution result
  hmp-commands: Remove the deprecated usb_add and usb_del

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