Support 'sudoers' database
Starting in sudo 1.7.0, support has been added to allow ordering of sudo
lookups using the nsswitch.conf file. This database option is not in the
standard nsswitch.conf documentation.

This commit adds the 'sudoers' database as one of the managed lines in
the nsswitch.conf file. This makes 'sudoers' technically the 16th
supported database.