rename old config object to TempestConfigPrivate

this attempts to make it clear to folks they should not be calling
this directly. The proxy is needed for lazy evaluation, so don't
call this.

Fix one issue where a config addition was landed before we got this
in tree.

Change-Id: I16eeee12aec4994c31a8bafdf12c7eddc98dff18
remove unneeded __init__ file

now that we got the constants out of load time, we can get rid
of this init file as it's basically a no-op.

Change-Id: I7815f83ea5a4702a6722e6433aece7b572cb78a9
remove last errant file parse warning

provide a way to be able to instantiate the config object without
parsing a config file. This is expected to only be used for the
config file generator comparitor.

This means we finally don't generate warning messages on config
file parsing during our pep8 runs, and we do the right thing and
explode during tests if the config file doesn't exist in a real
way.

Change-Id: Ic4ae22814e2fdafc89a1997471283ccf8f3663bc