change response code of error to http 500

Tribler/Core/Modules/restapi/my_channel_endpoint.py

@@ -96,6 +96,7 @@ def render_PUT(self, request):
         try:
             channel_id = self.session.create_channel(parameters['name'][0], parameters['description'][0], mode)
         except DuplicateChannelNameError as ex:
+            request.setResponseCode(http.INTERNAL_SERVER_ERROR)
             request.setHeader('Content-Type', 'text/json')
             return json.dumps({
                 "error": {

Tribler/Test/Core/Modules/RestApi/test_my_channel_endpoints.py

@@ -115,7 +115,7 @@ def verify_channel_created(body):
     @deferred(timeout=10)
     def test_my_channel_endpoint_create_duplicate_name_error(self):
         """
-        Testing whether the API returns a formatted 200 error if DuplicateChannelNameError is raised
+        Testing whether the API returns a formatted 500 error if DuplicateChannelNameError is raised
         """
 
         def verify_error_message(body):
@@ -136,8 +136,8 @@ def verify_error_message(body):
         }
         self.session.create_channel = self.create_fake_channel_with_existing_name
         self.should_check_equality = False
-        return self.do_request('mychannel', expected_code=200, expected_json=None, request_type='PUT',
-                               post_data=post_data).addCallback(verify_error_message)
+        return self.do_request('mychannel', expected_code=500, expected_json=None, request_type='PUT',
+                               post_data=post_data).addErrback(verify_error_message)
 
     @deferred(timeout=10)
     def test_my_channel_endpoint_create_no_name_param(self):

doc/Tribler REST API.md

@@ -24,7 +24,7 @@ If an unhandled exception occurs the response will have code HTTP 500 and look l
     }
 }
 ```
-If a valid request of a client caused a recoverable error the response will have code HTTP 200 and look like this:
+If a valid request of a client caused a recoverable error the response will have code HTTP 500 and look like this:
 ```json
 {
     "error": {