public Builder projectProperties(Properties projectProperties) {
                context.projectProperties = projectProperties;
                return this;
            }
Return a list of providers which could delive connection parameters from
calling external commands. For this plugin this is docker-machine, but can be overridden
to add other config options, too.

@return list of providers or <code>null</code> if none are applicable
src/main/java/io/fabric8/maven/docker/service/DockerAccessFactory.java