Merge remote-tracking branch 'remotes/cohuck/tags/boot-serial-no-tcg-20170811' into...

Fix the boot-serial test to work with the new --disable-tcg.

# gpg: Signature made Fri 11 Aug 2017 14:55:15 BST
# gpg:                using RSA key 0xDECF6B93C6F02FAF
# gpg: Good signature from "Cornelia Huck <[email protected]>"
# gpg:                 aka "Cornelia Huck <[email protected]>"
# gpg:                 aka "Cornelia Huck <[email protected]>"
# gpg:                 aka "Cornelia Huck <[email protected]>"
# gpg:                 aka "Cornelia Huck <[email protected]>"
# Primary key fingerprint: C3D0 D66D C362 4FF6 A8C0  18CE DECF 6B93 C6F0 2FAF

* remotes/cohuck/tags/boot-serial-no-tcg-20170811:
  boot-serial-test: fallback to kvm accelerator

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