tests/acceptance: bound the size of readline in s390_ccw_virtio
The read binary data as text via a PPM export of the frame buffer
seems a bit sketchy and it did blow up in the real world when the
assertion failed:
https://gitlab.com/qemu-project/qemu/-/jobs/
943183183
However short of cleaning up the test to be more binary focused at
least limit the attempt to dump the whole file as hexified zeros in
the logs.
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Willian Rampazzo <willianr@redhat.com>
Acked-by: Halil Pasic <pasic@linux.ibm.com>
Acked-by: Thomas Huth <thuth@redhat.com>
Message-Id: <
20210105124405.15424-1-alex.bennee@linaro.org>