s390x/smp: fix detection of "running"

On s390x hosts with a single CPU, the smp test case hangs (loops).
The check if our restart has finished is wrong.
Sigp sense running status checks if the CPU is currently backed by a
real CPU. This means that on single CPU hosts a sigp sense running
will never claim that a target is running. We need to check for not
being stopped instead.

Reviewed-by: Janosch Frank <frankja@linux.vnet.ibm.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Message-Id: <20200330084911.34248-2-borntraeger@de.ibm.com>
Signed-off-by: David Hildenbrand <david@redhat.com>