UBUNTU: SAUCE: kvm: Add helper function for creating VM worker threads

UBUNTU: SAUCE: kvm: Add helper function for creating VM worker threads

This adds a function to create a kernel thread associated with a given
VM. In particular, it ensures that the worker thread inherits the
priority and cgroups of the calling thread.

Signed-off-by: Junaid Shahid <junaids@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
CVE-2018-12207

[tyhicks: Backport to 4.15
 - Fix up conflicts in #includes of kvm_main.c
 - Minor context adjustments in kvm_host.h]
Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>