Graceful handling of being unable to bind

[mzedeler]

Binding to the samba related ports (137-139 and 445) in https://github.com/SvenDowideit/dockerfiles/blob/master/samba/setup.sh#L116-L119 doesn't necessarily work because there may be something else listening on those ports.

I suggest two fixes:

• Making sure to report it as an error if they are already taken.
• Making it possible to specify some other interface that the container should listen on.

I can provide a patch to fix both, if you want it.