ConfigDriveBuilder refactor for tempdir cleanliness

In looking to clean up excessive DEBUG logging, it became clear
that the logging in ConfigDriveBuilder was largely based on the
split logic that existed in doing fs opts in __init__ and then
also later in make_drive. This required a persistent tempdir, which
had to be manually cleaned up. It also meant a mandatory additional
config variable.

Refactor ConfigDriveBuilder to move all fs opts into make_drive,
deprecating the config variable in the process. In doing so, I don't
believe the previous debug logging is useful any more. However, in
case, add a __repr__ for ConfigDriveBuilder that will provide us with
a reasonable debug representation in case this becomes part of what
gets thrown.

Tests are now adjusted to not call private methods, but instead call
make_drive with config variable set.

Change-Id: I1aaf194fef00edd6eecf73b5bb9323e0e3a6f09f
Merge "ConfigDriveBuilder refactor for tempdir cleanliness"