This commit makes two changes to the provisioner connection block code:
- Change the `port` argument type from string to number, which is
technically more correct and consistent with `bastion_port`;
- Use `uint16` as the struct member type for both ports instead of
`int`, which gets us free range validation from the gocty package.
Includes a test of the validation message when the port number is an
invalid integer.
Alisdair McDiarmid