Unify backend logging

Make account, object, and container servers construct log lines using the
same utility function so they will produce identically formatted lines.

This change reorders the fields logged for the account server.

This change also adds the "additional info" field to the two servers that
didn't log that field.  This makes the log lines identical across all 3
servers.  If people don't like that, I can take that out.  I think it makes
the documentation, parsing of the log lines, and the code a tad cleaner.

DocImpact

Change-Id: I268dc0df9dd07afa5382592a28ea37b96c6c2f44
Closes-Bug: 1280955
Merge "Unify backend logging"
Fix deprecation warning

Accessing BaseException.message spews a warning; we can get the same
information with str(err), which does not spew.

Change-Id: I67648d53d25522be074a78c44b3ce97dc27d1f07