public static Map<String, String> extractFromPropertiesAsMap(String prefix, Properties properties) {
        Map<String, String> ret = new HashMap<>();
        Enumeration names = properties.propertyNames();
        String prefixP = prefix + ".";
        while (names.hasMoreElements()) {
            String propName = (String) names.nextElement();
            if (propMatchesPrefix(prefixP, propName)) {
                String mapKey = propName.substring(prefixP.length());
                if(PROPERTY_COMBINE_POLICY_SUFFIX.equals(mapKey)) {
                    continue;
                }

                ret.put(mapKey, properties.getProperty(propName));
            }
        }
        return ret.size() > 0 ? ret : null;
    }
Extract part of given properties as a map. The given prefix is used to find the properties,
the rest of the property name is used as key for the map.

NOTE: If key is "._combine"  it is ignored! This is reserved for combine policy tweaking.

@param prefix prefix which specifies the part which should be extracted as map
@param properties properties to extract from
@return the extracted map or null if no such map exists
src/main/java/io/fabric8/maven/docker/util/EnvUtil.java