KVM: selftests: VMX preemption timer migration test

When a nested VM with a VMX-preemption timer is migrated, verify that the
nested VM and its parent VM observe the VMX-preemption timer exit close to
the original expiration deadline.

Signed-off-by: Makarand Sonare <makarandsonare@google.com>
Reviewed-by: Jim Mattson <jmattson@google.com>
Message-Id: <20200526215107.205814-3-makarandsonare@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>