public FlavorsConfig build() {
        return new FlavorsConfig(builder);
    }
Simplifies creation of a node-repository config containing flavors.
This is needed because the config builder API is inconvenient.

Note: Flavors added will have fast disk and remote storage unless explicitly specified.

@author bratseth
node-repository/src/main/java/com/yahoo/vespa/hosted/provision/provisioning/FlavorConfigBuilder.java