system-test: Fixed several bashisms in populate script

system-test failed to compile on systems on which /bin/sh does not
point to bash (eg Debian and Ubuntu).

Also reformatted output to fit in 80-character terminal.

Target: trunk
Require-notes: no
Require-book: no
Acked-by: Paul Millar <paul.millar@desy.de>
Patch: http://rb.dcache.org/r/5752/