procps-ng : tests, remove which dependency

which is a separate package that may not be available and is not yet build on Linux from scratch build order.
Instead use posix command -v. command -v  is a builtin working with bash-4.2, 3.0.25 or even old bash-2.05 or current debian dash

Signed-off-by: Gilles Espinasse <g.esp@free.fr>

testsuite/config/unix.exp

@@ -117,7 +117,7 @@ proc make_testproc { } {
     set sleep_time 300
 
     set testproc_path [ exec mktemp -u ]
-    set sleep_path [ exec which sleep ]
+    set sleep_path [ exec sh -c "command -v sleep" ]
     exec ln -s $sleep_path $testproc_path
     set testproc_comm [ exec basename $testproc_path ]