oeqa/runtime: fix regression in minidebuginfo test

The builtin command "sleep" was getting executed instead of the busybox binary.
Hence "pidof sleep" was empty and the test was failing.

Signed-off-by: Etienne Cordonnier <ecordonnier@snap.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>