Merge pull request #344 from nathanielmanistaatgoogle/issue-334

Install PyPI's protobuf into the Python virtual environment.

tools/run_tests/build_python.sh

@@ -7,6 +7,5 @@ cd $(dirname $0)/../..
 
 root=`pwd`
 virtualenv python2.7_virtual_environment
-python2.7_virtual_environment/bin/pip install enum34==1.0.4 futures==2.2.0
-python2.7_virtual_environment/bin/pip install third_party/protobuf/python
+python2.7_virtual_environment/bin/pip install enum34==1.0.4 futures==2.2.0 protobuf==2.6.1
 python2.7_virtual_environment/bin/pip install src/python