private static File getTestPluginDir() {
        File targetDir = new File("target").getAbsoluteFile(); //$NON-NLS-1$
        if (!targetDir.isDirectory()) {
            throw new RuntimeException("Maven 'target' directory does not exist!"); //$NON-NLS-1$
        }
        File pluginDir = new File(targetDir, "plugintmp"); //$NON-NLS-1$
        try {
            FileUtils.deleteDirectory(pluginDir);
            pluginDir.mkdirs();
        } catch (IOException e) {
        }
        return pluginDir;
    }
Creates the temp directory to use for the plugin registry.  This will put
the temp dir in the target directory so it gets cleaned when a maven
build is done.
manager/test/api/src/main/java/io/apiman/manager/test/server/ApiManagerTestPluginRegistry.java