Correct arguments to logging function

ofctl_arg_supported contains a bad call to LOG.debug in an exception
path.

    LOG.debug("...%s. Exception: %s", (full_args, e))

This throws "TypeError: not enough arguments for format string" and
should be:

    LOG.debug("...%s. Exception: %s", full_args, e)

(Found via pylint)

Change-Id: Ib14666f60b16584f225b1e0c4fed82ef7e941aac
Closes-Bug: #1403296
Merge "Correct arguments to logging function"
Merge branch 'master' of https://github.com/openstack/quantum