Add a parameter to disable the automatic creation of krb5.conf files

Add a parameter to disable the automatic creation of krb5.conf files

This is necessary because MIT 1.5 can't deal with certain types (Tree Root) of
transitive AD trusts. The workaround is to add a [capaths] directive to
/etc/krb5.conf, which we don't automatically put into the krb5.conf winbind
creates.

The alternative would have been something like a "krb5 conf include", but I
think if someone has to mess with /etc/krb5.conf at this level, it should be
easy to add the site-local KDCs as well.

Next alternative is to correctly figure out the [capaths] parameter for all
trusted domains, but for that I don't have the time right now. Sorry :-)