samba_kcc: use new graph module for writing dot files

samba_kcc: use new graph module for writing dot files

We avoid changing the (annoying) signature of write_dot_file().

Using samba_kcc to write dot files may be deprecated.

Signed-off-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>