qemu-ga patch queue for hard-freeze

* fix leak in qga main loop error path
* better error reporting when Windows version doesn't support fstrim

# gpg: Signature made Tue 24 Jul 2018 00:58:29 BST
# gpg:                using RSA key 3353C9CEF108B584
# gpg: Good signature from "Michael Roth <flukshun@gmail.com>"
# gpg:                 aka "Michael Roth <mdroth@utexas.edu>"
# gpg:                 aka "Michael Roth <mdroth@linux.vnet.ibm.com>"
# Primary key fingerprint: CEAC C9E1 5534 EBAB B82D  3FA0 3353 C9CE F108 B584

* remotes/mdroth/tags/qga-pull-2018-07-23-tag:
  qga: process_event() simplification and leak fix
  qga-win: Handle fstrim for OSes lower than Win8

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