Enforced exit code 0 in prestart.sh

[mikaelhm]

This PR will fix the problem below, by ensuring that prestart.sh return a zero exit code on successful completion.

Problem:

prestart.sh will attempt to run test_collection/<collection_name>/prestart.sh if that script exists.

This is done by:

# Run Prestart scripts in test collections
for dir in ./test_collections/*
do
    prestart=$dir/prestart.sh
    # Only run prestart.sh if present/
    [ -x $prestart ] && $prestart
done

However, if the script doesn't exist. [ -x $prestart ] will return a non-zero value.
As this is the last step in prestart.sh the exit code of prestart.sh will be the non-zero value if the last iteration in the for-loop is for a test_collection that doesn't have a prestart script.

This will stop the start.sh to not start the gunicorn server.