fstests: per-test dmerror instances

fstests: per-test dmerror instances

We can't run two tests that use dmerror at the same time because
the device name is the same. hence they interfere with each other.
Give dmerror devices their own per-test names to avoid this
problem.

Note that we need a hack to pass the test sequence number through
to src/dmerror as used by generic/441 so that it can construct the
dmerror name correctly.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Zorro lang <zlang@redhat.com>
Signed-off-by: Zorro Lang <zlang@kernel.org>