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

* iothread bugfix (Eduardo)
* Linux headers sync (Dave)
* .gitignore fix (Eric)
* KVM capability check fixes (Greg)
* kvmclock fix (Jim)

# gpg: Signature made Mon 02 Oct 2017 14:31:09 BST
# gpg:                using RSA key 0xBFFBD25F78C7AE83
# gpg: Good signature from "Paolo Bonzini <bonzini@gnu.org>"
# gpg:                 aka "Paolo Bonzini <pbonzini@redhat.com>"
# Primary key fingerprint: 46F5 9FBD 57D6 12E7 BFD4  E2F7 7E15 100C CD36 69B1
#      Subkey fingerprint: F133 3857 4B66 2389 866C  7682 BFFB D25F 78C7 AE83

* remotes/bonzini/tags/for-upstream:
  kvmclock: use the updated system_timer_msr
  kvm: check KVM_CAP_NR_VCPUS with kvm_vm_check_extension()
  kvm: check KVM_CAP_SYNC_MMU with kvm_vm_check_extension()
  linux-headers: sync against v4.14-rc1
  iothread: Make iothread_stop() idempotent
  scsi: Ignore executable for in-tree builds

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