iotest 147 and 205 have recently been marked as "NBD-only", so they
are currently simply skipped and thus can be removed.

iotest 129 occasionally fails in the gitlab-CI, and according to Max,
there are some known issues with this test (see for example this URL:
https://lists.nongnu.org/archive/html/qemu-block/2019-06/msg00499.html

 ),
so for the time being, let's disable it until the problems are fixed.

The iotests 040, 127, 203 and 256 are scheduled to become part of "make
check-block", so we also do not have to test them seperately here anymore.

On the other side, new iotests have been added to the QEMU repository
in the past months, so we can now add some new test > 256 instead.

Message-Id: <20200121131936.8214-1-thuth@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>