Hi,

Since environment variables are global, I think they should be prefixed by `LOCALSTACK_` in the docker image. For example `SERVICES` environment variable might conflict at some point with something else, so naming it `LOCALSTACK_SERVICES` would be nicer.

This could be optional to avoid breaking changes. Localstack would look for `LOCALSTACK_SERVICES` first, and if it's not defined would fallback to `SERVICES` just as today.

As far as I know, most (maybe all) official docker images do this. I think it's a good practice. See:
- https://hub.docker.com/_/postgres
- https://hub.docker.com/_/nginx
- https://hub.docker.com/_/mysql

Thanks.
global SERVICE_PORTS
    SERVICE_PORTS = service_ports or parse_service_ports()
    globs = globals()
    
    for key, value in iteritems(DEFAULT_SERVICE_PORTS):
        key_upper = key.upper().replace('-', '_')
        
        port_key = 'PORT_%s' % key_upper
        globs[port_key] = SERVICE_PORTS.get(key, 0)
        url = 'http%s://%s:%s' % ('s' if USE_SSL else '', LOCALSTACK_HOSTNAME, SERVICE_PORTS.get(key, 0))
        
        url_key = 'TEST_%s_URL' % key_upper
        globs[url_key] = url
        
        os.environ[url_key] = url
    
    os.environ['LOCALSTACK_HOSTNAME'] = LOCALSTACK_HOSTNAME
def service_port(service_key):
    return SERVICE_PORTS.get(service_key, 0)
populate_configs()
if os.environ.get('DEBUG', '').lower() in ('1', 'true'):
    logging.getLogger('').setLevel(logging.DEBUG)
    logging.getLogger('localstack').setLevel(logging.DEBUG)
INBOUND_GATEWAY_URL_PATTERN = ('%s/restapis/{api_id}/{stage_name}/%s{path}' %
    (TEST_APIGATEWAY_URL, PATH_USER_REQUEST))