Add multi-protocol support (tcp and udp at once)

This patch changes how 'etc_services' role configures protocols for
a service. By default, if no protocols are specified, both tcp and udp
protocol entries will be created. You can specify protocols to generate
using new 'item.protocols' list in a service definition.

You can still use 'item.protocol' key in service definitions, but this
should be considered as legacy and avoided, this syntax will be removed
in the future.