py3: Fix encoding and use sys.stdin.buffer

* exc.py: Encode body in response before calling replace over it.
* http.py: prepend the bytes literal to the empty string or else
  we hit bug 1342080 again in python 3.
* utils.py: Use sys.stdin.buffer in python 3.

Change-Id: Ieefb8c633658e507486438e5518c5d53e819027d

glanceclient/common/http.py

@@ -63,7 +63,7 @@ class _BaseHTTPClient(object):
         chunk = body
         while chunk:
             chunk = body.read(CHUNKSIZE)
-            if chunk == '':
+            if not chunk:
                 break
             yield chunk