Description of problem:
it is not possible to send JSON POST REST Request to  /containers/{id} endpoint of Decision Server.

JSON is supported only for provisioning api- E.g: create-container, list-containers, dispose-container and call-container.

but not for actual rule execution - i.e. fire all rules

Version-Release number of selected component (if applicable):
6.1.0

How reproducible:
always

Steps to Reproduce:
1. Send JSON command to the decision server, i.e.:
{"batch-execution":{"commands":[{"insert":{"out-identifier":"f1","return-object":true,"entry-point":"DEFAULT","object":{"com.esrx.ref.testproject.Bean1":{"name":"Robert"}}}},{"fire-all-rules":{"out-identifier":"myFireCommand"}}]}}

2. Server responds with:
<response type="FAILURE" msg="Error calling container SecondContainer: com.thoughtworks.xstream.io.StreamException:  : only whitespace content allowed before start tag and not { (position: START_DOCUMENT seen {... @1:1) "/>

Actual results:
JSON commands are not supported

Expected results:
JSON commands are supported

Additional info: