Provide Debian Edu RootCA certificate (pub key) for download. (Closes: #933183)

Adjust debian/debian-edu-config.fetch-ldap-cert to copy the rootCA file to the
web server directory at certificate generation time.

Adjust cf3/cf.finalize to care for the rootCA file as well.

Adjust cf3/cf.workarounds to copy the rootCA file to the web server directory
upon main server upgrade.

Signed-off-by: Wolfgang Schweer <wschweer@arcor.de>