register_signal default value fix

This fixes a problem when calling register_signal() without specifying optional argument "own_hander"

Without this fix we get an exception like:

TypeError: register_signal(): incompatible function arguments. The following argument types are supported:
                1. (self: tango._tango.DeviceImpl, signo: typing.SupportsInt, own_handler: bool) -> None

Replaces !958 (closed)