netcmd: simplify boolean check

Should use "is" for checking booleans rather than "==" in Python, however these can also be simplified.

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