Move antlr3 from the front to the back of sys.path

Adding antlr3 to the front of sys.path causes confusion for subsequent
imports.  I ran into a problem where "import extras" imported something from
the antlr3 directory instead of site-packages.  Antlr3 should be at the back
of the sys.path.

Change-Id: I03c4f723236c1b99759fa9d03f6296f4e49f98db
Merge "Move antlr3 from the front to the back of sys.path"