Do not format messages before they are logged

The python logging facility allows for the logging message to contain
string formatting commands, and will format that string with any
additional arguments provided. It will only perform this formatting if
the logging level allows.

So if you have:

   A. logging.debug("this %s that %s", this, that)
   B. logging.debug("this %s that %s" % (this, that))

Then A only formats the message if the debug logging level is set,
where as B will always format the message. Since this filter is often
on the fast-path for swift requests, it will help the small object
case to avoid any extra possible work.

Change-Id: I51414dc6577df50d5573a0f917e0656c4ae99520
Merge "Do not format messages before they are logged"