tests/qemu-iotests/check: Replace "tests" with "iotests" in final status text

tests/qemu-iotests/check: Replace "tests" with "iotests" in final status text

When running "make check -j8" or something similar, the iotests are
running in parallel with the other tests. So when they are printing
out "Passed all xx tests" or a similar status message at the end,
it might not be quite clear that this message belongs to the iotests,
since the output might be mixed with the other tests. Thus change the
word "tests" here to "iotests" instead to avoid confusion.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-id: 20190906113920.11271-1-thuth@redhat.com
Reviewed-by: John Snow <jsnow@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>