fix: stream request data rather than loading it into memory

Change-Id: I47b1791de2a3d21b578604c1ea56f751cdb366ad
Closes-Bug: 1230388

marconi/proxy/utils/helpers.py

@@ -52,7 +52,7 @@ def forward(host, request):
     method = request.method.lower()
     resp = requests.request(method, url,
                             headers=canonicalize(request._headers),
-                            data=request.stream.read())
+                            data=request.stream)
     return resp