Fixed an error preventing Thrift::NonblockingServer from working with SSL

[kpumuk]

Currently Thrift::NonblockingServer does not work when configured with SSL sockets:

$ THRIFT_TLS=true bundle exec rake benchmark /usr/local/bin/ruby benchmark/benchmark.rb
Starting server...
#<Thread:0x0000ffff817cb718 benchmark/server.rb:87 run> terminated with exception (report_on_exception is true):
/thrift/src/lib/rb/lib/thrift/server/nonblocking_server.rb:48:in 'Kernel#select': can't convert Thrift::SSLServerSocket to IO (Thrift::SSLServerSocket#to_io gives OpenSSL::SSL::SSLServer) (TypeError)

            rd, = select([@server_transport], nil, nil, 0.1)
                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        from /thrift/src/lib/rb/lib/thrift/server/nonblocking_server.rb:48:in 'block in Thrift::NonblockingServer#serve'
        from /thrift/src/lib/rb/lib/thrift/server/nonblocking_server.rb:45:in 'Kernel#loop'
        from /thrift/src/lib/rb/lib/thrift/server/nonblocking_server.rb:45:in 'Thrift::NonblockingServer#serve'
        from benchmark/server.rb:88:in 'block in Server.start_server'

This is happening because #to_io on the SSL socket returns the wrapped handler instead of the underlying socket.

After the change we get a clear output:

$ THRIFT_TLS=true bundle exec rake benchmark
/usr/local/bin/ruby benchmark/benchmark.rb
Starting server...
Spawning benchmark processes...
Collecting output...
Translating output...
Analyzing output...

Server class:        Thrift::NonblockingServer
Server interpreter:  ruby 
Client interpreter:  ruby
Protocol type:       binary
Socket class:        Thrift::SSLSocket 
Number of processes: 40
Clients per process: 5
Calls per client:    50
Using fastthread:    no

Connection failures:                0 
Connection errors:                  0
Average time per call:              0.0033 seconds
Average time per client (50 calls): 0.2159 seconds
Total time for all calls:           32.5091 seconds
Real time for benchmarking:         2.7874 seconds
Shortest call time:                 0.0001 seconds
Longest call time:                  0.0213 seconds
Shortest client time (50 calls):    0.0560 seconds
Longest client time (50 calls):     0.3463 seconds

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