samba-tool: avoid mutable Command class values
These values are shared across all instances of the class,
which makes no difference in samba-tool itself, because there
is one instance per process. But in tests we can have many
Command classes at once (due to runcmd()), and if any of them
happened to append to takes_args or takes_options rather than
replacing it, well, the effect would be subtle.
Signed-off-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>