set lowercase os[:family] for OpenBSD

this is consistent with other os'es and adheres to the principle of least astonishment
Implement check_has_ipv6_address for OpenBSD
Merge pull request #221 from jasperla/family_openbsd

set lowercase os[:family] for OpenBSD
Merge pull request #222 from jasperla/ipv6_address_openbsd

Implement check_has_ipv6_address for OpenBSD
Bump up version