VOL-1449 Modify build environment to use pyvoltha

Depending on if LOCAL_PYVOLTHA is set use a build of
the library from the nearby source tree, for both
virtualenv and docker image builds.  By default
requirements.txt uses the pip hosted dev build, which
may not be new enough for iterative development

Also by setting PYVOLTHA_BASE_IMAGE use a docker image produced
by pyvoltha as the base image.

Change-Id: Ibf7218b92450f92d6a3f1c9d837be46fcc3a84db
diff --git a/python/requirements.txt b/python/requirements.txt
index 56cb356..015660e 100644
--- a/python/requirements.txt
+++ b/python/requirements.txt
@@ -60,10 +60,6 @@
 etcd3==0.7.0
 pyparsing==2.2.0
 packaging==17.1
-
-# python-consul>=0.6.1  we need the pre-released version for now, because 0.6.1 does not
-# yet support Twisted. Once this is released, it will be the 0.6.2 version
-git+https://github.com/cablehead/python-consul.git
-
-# Twisted Python kafka client
-git+https://github.com/ciena/afkak.git
+python-consul==0.6.2
+afkak==3.0.0.dev20181106
+pyvoltha==0.1.7