helpers/new_release: fix with new lists git-hash format

The git-hash file for lists now has the same format as for packages. Thus we have to test it separately as well as to extract hash from it using the same function. It is also now specified in feeds.conf file so we have to set appropriate has to it as well.

This also adds set -eu to the script to make it more resilient. There is also a tweak of indentation.

Fixes #305 (closed)