Add support for stdapi_net_resolve_host.
Add fault tolerance for resolve_hosts.
Return nil on error, and move the module to post/multi.
Remove windows from title of multi module.
Land #2453, Add stdapi_net_resolve_host(s) to Python Meterpreter.

Moves resolve_host post module to multi and depreciates Windows module.
Resolve will now return nil for failed lookups instead of an empty
string.