bin: nitc does no more rely on procfs

Signed-off-by: Jean Privat <jean@pryen.org>
toolcontext: nit_der tries another heuristic on PATH is procfs is not available

Signed-off-by: Jean Privat <jean@pryen.org>
tests: fix saferun() return value when TIME is not not

Signed-off-by: Jean Privat <jean@pryen.org>