Encapsulate logger within GRPC module

src/ruby/bin/apis/pubsub_demo.rb

src/ruby/bin/interop/interop_client.rb

src/ruby/bin/interop/interop_server.rb

src/ruby/bin/math_client.rb

src/ruby/bin/math_server.rb

src/ruby/bin/noproto_client.rb

src/ruby/bin/noproto_server.rb

src/ruby/lib/grpc/generic/active_call.rb

src/ruby/lib/grpc/generic/bidi_call.rb

src/ruby/lib/grpc/generic/rpc_desc.rb

src/ruby/lib/grpc/generic/rpc_server.rb

src/ruby/lib/grpc/generic/service.rb

src/ruby/lib/grpc/logconfig.rb

src/ruby/spec/generic/rpc_server_spec.rb