Replace antlr3 symlinking by sys.path
Replace antlr3 symlinking by sys.path

For importing the correct antlr3 runtime depending on python version,
use sys.path instead of creating and deleting symlinks

Purpose: Reduce fragility and OS dependence

Partially implements blueprint: support-python3

Change-Id: I4e5fda406f77b7902bfd21bff3aeef33a0c4faa0

openstack/congress,ramineni/my_congress,ramineni/my_congress,openstack/congress,ramineni/my_congress,ramineni/my_congress