ring.rb: specify multicast interface

* lib/rinda/ring.rb (Rinda::RingServer#initialize): accept array
  arguments of address to specify multicast interface.

* lib/rinda/ring.rb (Rinda::RingServer#make_socket): add optional
  arguments for multicast interface.

* test/rinda/test_rinda.rb
  (TestRingFinger#test_ring_server_ipv4_multicast,
   TestRingFinger#test_ring_server_ipv6_multicast): add tests for
  above change.

* test/rinda/test_rinda.rb
  (TestRingServer#test_make_socket_ipv4_multicast,
   TestRingServer#test_make_socket_ipv6_multicast): change bound
  interface address because multicast address is not allowed on Linux
  or Windows.
  [ruby-core:53692] [Bug #8159]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@40472 b2dd03c8-39d4-4d8f-98ff-823fe69b080e