THRIFT-1914 Python: Support for Multiplexing Services on any Transport

copy patch from: https://issues.apache.org/jira/browse/THRIFT-1914 add some testcases.

add new options `multiple`, if set `True`, will test  `ThriftTest` and `SecondService`.

run server:

    $ python TestServer.py --port=9999 --multiple -v TSimpleServer

run client:

    $ python TestClient.py --host=127.0.0.1 --port=9999 --multiple
    ...................
    ----------------------------------------------------------------------
    Ran 19 tests in 0.693s

    OK