Common yang and xml loader for tests

Common yang and xml loader for tests

Class YangAndXmlAndDataSchemaLoader was created as common ancestor for
those test which need load yang files, get reference to concrete module
and concrete schema node.

DummyRpcResult class was transformed (inner Builder class including) to
generic class. Type parameter represents return type of method getResult.
Now it is possible to use DummyRpcResult also in InvokeRpcMethodTest.

Change-Id: Ib8d99596bbb16c42724ab79125f4273f9d609a50
Signed-off-by: Jozef Gloncak <jgloncak@cisco.com>