Raise number of nailgun uWSGI workers and sockets

Fixes issue where nailgun stops responding to requests
because all workers are occupied and the queue of
available uWSGI sockets fills up by increasing the
number of workers (double) and raising the connection
limit from 100 to 4096.

Closes-Bug: #1391935

Change-Id: Id6bb0fc259ee78fa5dc33ce072ba426e595278f7
(cherry picked from commit e2e1166a55f2dea80ed29dc37ebcaed93f8122c3)
Merge "Raise number of nailgun uWSGI workers and sockets" into stable/5.1