THRIFT-2881 Handle errors from Accept() correctly

Often in tests, servers are started and closed when a test case is
finished, as in the standard library's "httptest" package.

http://golang.org/pkg/net/http/httptest/#example_Server

However, currently the "p.quit" channel of TSimpleServer does not
correctly handle the case when the listener socket is Closed, resulting
in spurious logs with the text "Accept err: ...".
For details of handling closed listener sockets, see

https://code.google.com/p/go/issues/detail?id=4373
http://zhen.org/blog/graceful-shutdown-of-go-net-dot-listeners/
http://stackoverflow.com/a/13419724/2182406