Do not translate debug messages

LOG.debug messages do not need to be translated. The rdb driver
has a couple of debug messages that are translated. This patch
removes those debug translations.

Also, logging exception.ImageUnacceptable can contain non-ascii
characters. This patch fixes this by using six.text_type to
properly translate the exception.

Change-Id: I4ed36173f42b7bf487463f148ae94bd061f6bebb
Merge "Do not translate debug messages"