Style improvements to logging format strings

Added the following improvements:

* Use the logging API to handle formatting of message args, which
  potentially prevents us from having to do a bunch of redundant string
  formatting for logging statements which occur below the runtime's
  logging level. For example, in many places `LOG.debug('foo %s' % bar)`
  has been replaced with `LOG.debug('foo %s', bar)`.
* Similarly, this change also removes a few redundant repr() and str()
  calls. For example: `LOG.error('foo %r', repr(bar))` ->
  `LOG.error('foo %r', bar)`, and the same for %s/str().
* One logging statement included some unnecessary escaping in the log
  message string (e.g., 'foo is a \'bar\'', which was replaced with
  "foo is a 'bar'").

Change-Id: I9080aebdf0ce0e719949d009e0ab85bfc6be8646
Closes-Bug: #1234283