python: Make the unit tests run faster and more reliably

python: Make the unit tests run faster and more reliably

- The async test was making the server sleep for 2 seconds.  Cut it to 0.5.
- The test driver was waiting 5 seconds for shutdown.  Cut it to 1.
- Add a 0.25 second sleep to make sure the server comes up before the client.

This is all a bit hacky, but it is better than the status quo.

git-svn-id: https://svn.apache.org/repos/asf/incubator/thrift/trunk@739628 13f79535-47bb-0310-9956-ffa450edef68