Remove str() from LOG.* and exceptions

gettextutils is expecting to receive unicode strings
rather than basestrings.  A basestring can cause an
unhandled exception in the logging code.  To help avoid
such issues we should remove str() from LOG.* messages and
exceptions.  We have verified that the %s formatting code
properly handle getting strings to unicode where necessary.

This patch also fixes one case where a message object was
being concatenated with '+' .  This, like using str() will
cause logging to fail and needs to be fixed.

See bug https://bugs.launchpad.net/cinder/+bug/1274245 for
the original discussion of this problem.

Fix for oslo.messaging: https://review.openstack.org/90577

Change-Id: Iad7c2284c6b21322b96dc881a82bbbab4ebb208e
Closes-bug:  1286306
Merge "Remove str() from LOG.* and exceptions"