Use application/json for upload REST api

Upload REST api body is empty, but since this is REST api, so use
"Content-Type: application/json" instead of "text/html; charset=utf-8"

[We want to use a json response instead of using HTTP headers?]

src/bepasty/apis/rest.py

@@ -79,6 +79,8 @@ def update_item(self, item, name):
 
         # Make a Response and create Transaction-ID from ItemName
         response = make_response()
+        response.headers['Content-Type'] = 'application/json'
+        response.data = '{}'
         name_b = name if isinstance(name, bytes_type) else name.encode()
         trans_id_b = base64.b64encode(name_b)
         trans_id_s = trans_id_b if isinstance(trans_id_b, str) else trans_id_b.decode()

src/bepasty/tests/test_rest_server.py

@@ -183,14 +183,14 @@ def check_data_response(response, meta, data, offset=0, total_size=None,
         assert data == response.data
 
 
-def check_json_response(response, metas, check_data=True):
-    check_response(response, 200, check_data=check_data)
+def check_json_response(response, metas, code=200, check_data=True):
+    check_response(response, code, check_data=check_data)
     if check_data:
         assert metas == response.json
 
 
 def check_upload_response(response, code=201, check_data=True):
-    check_response(response, code, 'text/html; charset=utf-8', check_data)
+    check_json_response(response, {}, code=code, check_data=check_data)
 
     if code == 200:
         assert len(response.headers[TRANSACTION_ID]) > 0