samba-tool visualize for understanding AD DC behaviour

To work out what is happening in a replication graph, it is sometimes
helpful to use visualisations. We introduce a samba-tool subcommand to
write Graphviz dot output and generate text-based heatmaps of the
distance in hops between DCs.

There are two subcommands, two graphical modes, and (roughly) two modes of
operation with respect to the location of authority.

`samba-tool visualize ntdsconn` looks at NTDS Connections.
`samba-tool visualize reps` looks at repsTo and repsFrom objects.

In '--distance' mode (default), the distances between DCs are shown in
a matrix in the terminal. With '--color=yes', this is depicted as a
heatmap. With '--utf8' it is a lttle prettier.

In '--dot' mode, Graphviz dot output is generated. When viewed using
dot or xdot, this shows the network as a graph with DCs as vertices
and connections edges. Certain types of degenerate edges are shown in
different colours or line-styles.

Normally samba-tool talks to one database; with the '-r' (a.k.a.
'--talk-to-remote') option attempts are made to contact all the DCs
known to the first database. This is necessary to get sensible results
from `samba-tool visualize reps` because the repsFrom/To objects are
not replicated, and it can reveal replication issues in other modes.

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

python/samba/netcmd/main.py

@@ -76,3 +76,4 @@ class cmd_sambatool(SuperCommand):
     subcommands["time"] = None
     subcommands["user"] = None
     subcommands["processes"] = None
+    subcommands["visualize"] = None