[JAVA] Refs with depth greater than 2 are not resolved properly

Description

Refs having file depth greater than 2 are not resolved properly.

Swagger-codegen version

2.4.6

Swagger declaration file content or url

First file (test.yaml)

definitions:
  test:
    type: 'object'
    properties:
      test:
        $ref: 'test2.yaml#/definitions/MyTestCluster'

Second file (test2.yaml)

definitions:
  MyTestCluster:
    $ref: 'test3.yaml#/definitions/my.test.Cluster'

Third file (test3.yaml)

definitions:
  my.test.Cluster:
      type: 'object'
      properties:
        value:
          type: 'integer'
          format: 'int64'

Command line used for generation

java -jar swagger-codegen-cli.jar generate -l java -i test.yaml -o out/

Steps to reproduce

Create 3 files with refs chaining from the first file to the third and try to generate java code.

Suggest a fix/enhancement

Will try to debug, for now it look like there's a problem in DefinitionsProcessor.processDefinitions method.

Start with DefinitionsProcessor.processDefinitions and reproduce the issue using the three linked YAML files and the Java generation command. Trace the chained refs from test.yaml through test2.yaml to test3.yaml; done means the third-level definition resolves and Java code generation succeeds.