All response headers are now exposed as unicode objects. Any
url-encoding is interpretted as UTF-8; if that causes decoding to fail,
the url-encoded form is returned.
As a result, deleting DLOs with unicode characters will no longer raise
UnicodeEncodeErrors under Python 2.
Related-Bug: #1431866
Change-Id: Idb111c5bf3ac1f5ccfa724b3f4ede8f37d5bfac4