tests: Wait for migration completion on destination QEMU to avoid failures

tests: Wait for migration completion on destination QEMU to avoid failures

Rather than waiting for the completion of migration on the source side,
wait for it on the destination QEMU side to avoid accessing the TPM TIS
memory mapped registers before QEMU could restore their state. This
error condition could be triggered on busy systems where the destination
QEMU did not have enough time to restore the TIS state while the test case
was already reading its registers. The test case was for example reading
the STS register and received an unexpected value (0xffffffff), which
lead to a segmentation fault later on due to trying to read 0xffff bytes
from the TIS into a buffer.

Cc:  <qemu-stable@nongnu.org>
Reported-by: Fabiano Rosas <farosas@suse.de>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>