Windows: Save Wix config at start if possible

Windows: Save Wix config at start if possible

Save the current configuration at the start of the install
process so the user can be presented with a dialog prior
to installation asking whether the existing or saved
configuration should be used or whether a new configuration
should be created.

Reviewed-on: http://gerrit.openafs.org/5281
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>
Tested-by: Jeffrey Altman <jaltman@openafs.org>
(cherry picked from commit 020b415be8fa357cded6eb4c50454aaa5b0722bf)

Change-Id: I49abfa6d6e7b929e3880686f7dc7bad4175adcba
Reviewed-on: http://gerrit.openafs.org/5284
Reviewed-by: Derrick Brashear <shadow@dementix.org>
Tested-by: Derrick Brashear <shadow@dementix.org>