samba-tool visualize ntdsconn: add --importldif option

samba-tool visualize ntdsconn: add --importldif option

This visualizes the NTDSConnections in an LDIF file exported via
`samba_kcc --exportldif`. This functionality is already available in a
roundabout way -- you can use `samba_kcc --import_ldif`, and use the
DB that generates. This just shortens the process.

The ldif import/export feature is useful for analysing AD networks
offsite without exposing too much sensitive data.

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