Actually set Chef::Config values in auto-configure code.

This code should be factored out into a common method.  It was correct
in the backup script but incorrect in the restore script.

Fixing this allows knife ec restore to work without a config file in
the default case.
Add id to key export and call key import/export from restore/backup

Restoring the user id ensures that USAGs still work as expected,
provided that the user id is restored before the groups.

This commit adds --with-user-sql to call the key export/import
functions from the backup and restore commands.  Sequel is required
very late so the tool can still be used without it if desired.
Add --[no-]skip-user-ids option to support earlier use pattern.