Wrong warn log signature in jboss-kie-modules and output on bats file

The internal test scripts from jboss-kie-modules project are calling the function log_warn from logging.sh with log_warning signature, which is leading to errors like command not found.

The functions from the jboss-kie-common heavily uses this function, which can make a mess with the return value if outside a Kubernetes environment. A suggestion to fix this is:

1. Change the function name to log_warning
2. To not make a mess with the stdout (which is used to return values from functions), redirect the warn and error messages to stderr, like:

function log_warning() { 
    echo "[WARN]"$1 >&2 
}