netcmd: Change Py3 incompatible long() for tombstone expunge

netcmd: Change Py3 incompatible long() for tombstone expunge

The code to expunge tombstones uses long(), which is not Python3
compatible. Python3 uses int() instead, and works out how big it needs
to be.

As long as we don't run the samba-tool command on a 32-bit machine
after the year 2038, then we should avoid any integer overflow on
Python 2.x.

Signed-off-by: Tim Beale <timbeale@catalyst.net.nz>
Reviewed-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Reviewed-by: Gary Lockyer <gary@catalyst.net.nz>