Sanitize output

Signed-off-by: Etienne Millon <me@emillon.org>

test/blackbox-tests/test-cases/cram/git-diff-fail.t

@@ -18,7 +18,8 @@ We need to avoid the special treatment of the test when INSIDE_DUNE is set:
 We do not observe the leaking of the display of internal processes when running
 dune build. Note that we scrub the actual reported error due to the build tool
 being bogus.
-  $ dune build --root=. --diff-command="exit 1; echo" --display=short @runtest | sed '/^(cd/d' 
+
+  $ bash -c 'set -o pipefail; dune build --root=. --diff-command="exit 1; echo" --display=short @runtest 2>&1 | grep -v "(cd"'
   File "mytest.t", line 1, characters 0-0:
   Command exited with code 1.
   [1]