Finalize Python3 support

Set the environment variable PYTHONHASHSEED to 0 to have
predictive tests under Python 3.

Change-Id: Ia15a9383e0f20bd0e4572e9f9b9772f1704dff86

glanceclient/common/utils.py

@@ -267,7 +267,8 @@ def get_file_size(file_obj):
     :param file_obj: file-like object.
     :retval The file's size or None if it cannot be determined.
     """
-    if hasattr(file_obj, 'seek') and hasattr(file_obj, 'tell'):
+    if (hasattr(file_obj, 'seek') and hasattr(file_obj, 'tell') and
+            (six.PY2 or six.PY3 and file_obj.seekable())):
         try:
             curr = file_obj.tell()
             file_obj.seek(0, os.SEEK_END)