KVM: s390: add stop_on_stop flag when doing stop and store

When we do a stop and store status we need to pass ACTION_STOP_ON_STOP
flag to __sigp_stop().

Signed-off-by: Jens Freimann <jfrei@linux.vnet.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>