Based on feedback on the sme-integration list we should support setting a maven proxy via an ENV setting. Seems like it's a common thing requirement and it's varies by environment.

I don't want it to clash with the configuration/settings.xml approach tho. So perhaps generate a settings.xml from the ENV vars and set it via '-global-settings' and configure the configuration/settings.xml via the '-settings' option. Hopefully both go into effect then.