Add a delay between process launches.

It so happens that the client process was launched before the server causing
deadlocks in some cases. Fixed that by adding a small delay. In reality, we may
need to logic to vtkTestDriver to make it more featured and parse outputs from
processes to handle this correctly. We can do that in next stage.

Change-Id: Ief6989c50e816bc8b6b7f8a780fd31b578079f4c
Merge topic 'fix_socket_test' into master

4c3786b0 Add a delay between process launches.