pin python-engineio to 2.3.2 as recent 3.0.0 update breaks gevent #1995

As of 25th November 2018 source builds failed to display live Web-UI
header info such as time, Rockstor and kernel version etc. This was
tracked down to an upstream python-engineio updated to 3.0.0. Although
this update may not be the direct cause, pinning it's version to the
latest prior released resolved the observed regressions.

setup.py

@@ -71,6 +71,7 @@
         'django-pipeline == 1.6.9',
         'django-ztask == 0.1.5',
         'djangorestframework == 3.1.1',
+        'python-engineio == 2.3.2',  # Revisit version post 3.0.0
         'gevent == 1.1.2',
         'gevent-websocket == 0.9.5',
         'mock == 1.0.1',