Replace bash with sh

Cromwell assumes that bash is available and uses it to execute the wrapper script to housekeep files and globs before and after the execution of the actual command. However, some docker images (for example, alpine) has a different shell by default and only provide bash after explicit installation.

It seems that the script comprises rudimentary commands and pipes and a full-fledged bash is not really needed. Check whether the simple /bin/sh can be used instead.