Clean the test cases for service plugins

Make HTTPRequestV3 to HTTPRequest in test_services functions.

Partially implements blueprint v2-on-v3-api

Change-Id: I8e96060051f1ef3e037602007a2bf127f9b334ee
Add API validation schema for services v2.1 plugin

This patch adds API validation schema for 'services' plugin
for V2.1.

Partially implements blueprint v2-on-v3-api

Change-Id: Ife11459bf53e097b0bd21e008785a5222eff0092
Merge "Clean the test cases for service plugins"
Merge "Add API validation schema for services v2.1 plugin"