ApiDiscovery: Fix response and service impl to make them test-able
plugins: Indentation fix for pom.xml, add build/test rules for api discovery

Signed-off-by: Rohit Yadav <bhaisaab@apache.org>
ApiDiscovery: Add mockito, unit test for ApiDiscovery service impl

Signed-off-by: Rohit Yadav <bhaisaab@apache.org>