4869: Improve logging
4869: KeepClient now has a default timeout per block request (10 minutes).  In
keepproxy, the timeout is set to 20 seconds per block.  Also rearranged some
keepclient and keepproxy logging to provide better information.
4869: Keepstore now returns Content-Length headers, and logs the error message
sent to the client on errors.
4869: Correctly handle zero-length blocks in Keep client/Keep proxy.  Remove
X-Block-Size.  Choose default request timeout based on if client is talking to
a proxy or not.  Use double quotes in logging.  Rename "tag" to "requestId".
4869: Based on Go documentation, don't set a body ReadCloser on the request
when body length is 0.
4869: Strip all newlines from error responses, not just leading and trailing
whitespace.
Merge branch '4869-keepproxy' refs #4869