Fixes docstring at eventlet_server

The WSGI server is a normal process (not a thread as being
described in the docstring), it uses a green thread pool though,
to handle upcoming jobs.

Change-Id: I688175eeaccd4c1aa4b2ee5564745b502b9cb748
Closes-Bug: 1380477
Merge "Fixes docstring at eventlet_server"