Improve fix for issue 47 using prep -x -o
Improve fix for issue 47 using prep -x -o

The use of `pgrep -x`was proposed by @rnelson0. `pgrep -x -o` should limit the result to the oldest exactly matching execution of a binary called `docker`.

Signed-off-by: Joachim Lusiardi <d67e61224e0469ccabe7b3e5cdc4dc2003a62c23@lusiardi.de>

timperman/docker-bench-security,HuKeping/docker-bench-security,Sauraus/docker-bench-security,konstruktoid/docker-bench-security,iangelov/docker-bench-security,no2key/docker-bench-security,jumanjiman/docker-bench-security,docker/docker-bench-security,aaam/docker-bench-security,petersellars/docker-bench-security,diogomonica/docker-bench-security,gmanfunky/docker-bench-security,nicolaka/docker-bench-security,salmanbaset/docker-bench-security,amegianeg/docker-bench-security