[JAXRS] Format not respected for primitive datatype Definition models

Description

The format for a primitive datatype definition is not respected when referenced from other definitions or responses.

Swagger-codegen version

Originally seen in 2.3.0 but also in master

Swagger declaration file content or url

sample api.yml

swagger: '2.0'
info:
  title: 'Test'
  description:
  version: 0.0.1
  contact:
    name: 'justine'
basePath: /api/

paths:
  /test:
    get:
      operationId: test_operation
      produces:
        - application/json
      parameters: []
      responses:
        '200':
          description: successful operation
          schema:
            $ref: '#/definitions/Test'

definitions:
  Test:
    type: object
    properties:
      Long1:
        $ref: "#/definitions/LongProperty"

      Long2:
        type: integer
        format: int64

  LongProperty:
    type: integer
    format: int64

Generated Test model class (partial)

public class Test   {
  @JsonProperty("Long1")
  private Integer long1 = null;

  @JsonProperty("Long2")
  private Long long2 = null;

  public Test long1(Integer long1) {
    this.long1 = long1;
    return this;
  }
...
}

Command line used for generation

swagger-codegen generate -i api.yml -l jaxrs

Steps to reproduce

Copy paste example api.yml file
Run command line
Go to src/gen/java/io/swagger/model/Test.java and the Long1 field will be an Integer but the Long2 field is a Long.

Suggest a fix/enhancement

The format property should be respected for primitive datatype Definitions.

Start with api.yml and the JAXRS generation path invoked by swagger-codegen generate -i api.yml -l jaxrs; compare the generated src/gen/java/io/swagger/model/Test.java fields for Long1 and Long2. Trace how referenced primitive definitions are mapped and verify that the referenced LongProperty produces the same Java type as the inline int64 property.