Write CPAN config in root user as well.

While ceph-qa-chef is normally ran as ubuntu user (stuff ran as
root via sudo) the environment is still ubuntu's home directory.

During preseed/imaging ceph-qa-chef is ran as root and thus we
need to write the CPAN config files for both ubuntu and root.

Signed-off-by: Sandon Van Ness <sandon@inktank.com>