message: java adf, avoid unnecessary breaking changes in SDK
diff: ## Java
  These settings apply only when `--java` is specified on the command line.
  -Please also specify `--azure-libraries-for-java-folder=<path to the root directory of your azure-libraries-for-java clone>`.
  ``` yaml $(java)
  -azure-arm: true
  -fluent: true
  -namespace: com.microsoft.azure.management.datafactory
  -license-header: MICROSOFT_MIT_NO_CODEGEN
  -payload-flattening-threshold: 1
  -output-folder: $(azure-libraries-for-java-folder)/azure-mgmt-datafactory
  -```
  -
  -# Validation
  -
  -
  -### Java multi-api
  -
  -``` yaml $(java) && $(multiapi)
  -batch:
  - - tag: package-2017-09-preview
  - - tag: package-2018-06
  -```
  -
  -### Tag: package-2017-09-preview and java
  -
  -These settings apply only when `--tag=package-2017-09-preview --java` is specified on the command line.
  -Please also specify `--azure-libraries-for-java=<path to the root directory of your azure-sdk-for-java clone>`.
  -
  -``` yaml $(tag) == 'package-2017-09-preview' && $(java) && $(multiapi)
  -java:
  - namespace: com.microsoft.azure.management.datafactory.v2017_09_01_preview
  - output-folder: $(azure-libraries-for-java-folder)/sdk/datafactory/mgmt-v2017_09_01_preview
  -regenerate-manager: true
  -generate-interface: true
  -```
  -
  -### Tag: package-2018-06 and java
  -
  -These settings apply only when `--tag=package-2018-06 --java` is specified on the command line.
  -Please also specify `--azure-libraries-for-java=<path to the root directory of your azure-sdk-for-java clone>`.
  -
  -``` yaml $(tag) == 'package-2018-06' && $(java) && $(multiapi)
  -java:
  - namespace: com.microsoft.azure.management.datafactory.v2018_06_01
  - output-folder: $(azure-libraries-for-java-folder)/sdk/datafactory/mgmt-v2018_06_01
  -regenerate-manager: true
  -generate-interface: true
  +directive:
  +- from: datafactory.json
  + where: $.definitions.LinkedServiceReference.properties.type["x-ms-enum"]
  + transform: $["modelAsString"] = false
  ```
  