We pass *encoded* headers to log_curl_request, but then compare them to
*unencoded* sensitive headers that must be redacted (basically comparing
bytes to strings). This means no header is ever redacted.
Store sensitive headers as bytes rather than strings to fix this issue.
Change-Id: I06785704750e8c4b23d1276514949655e6dcb7ab
Closes-Bug: #2051712
28497adc33