private static void copySchemas(File from, File to) throws IOException {
        if (! from.exists()) throw new IOException("Could not find schema source directory '" + from + "'");
        if (! from.isDirectory()) throw new IOException("Schema source '" + from + "' is not a directory");
        File sourceFile = new File(from, servicesXmlSchemaName);
        if (! sourceFile.exists()) throw new IOException("Schema source file '" + sourceFile + "' not found");
        IOUtils.copyDirectoryInto(from, to);
    }
Looks for schema files in config-model.jar and saves them in a temp dir. Uses schema files
in $VESPA_HOME/share/vespa/schema/[major-version].x/ otherwise

@return the directory the schema files are stored in
@throws IOException if it is not possible to read schema files
config-application-package/src/main/java/com/yahoo/config/model/application/provider/SchemaValidators.java