Drop support for EOL Python 2.6 and 3.3

* Drop support for EOL Python 2.6

* Use more helpful assertIn/NotIn instead of assertTrue/False

* Drop support for EOL Python 3.3

* Remove redundant Python 3.3 code

* Restore code for RHEL 6 and virtualenv for Py2.7

* Revert pipstrap.py to upstream

* Merge py26_packages and non_py26_packages into all_packages

* Revert changes to *-auto in root

* Update by calling letsencrypt-auto-source/build.py

* Revert permissions for pipstrap.py

tests/letstest/scripts/test_tox.sh

@@ -15,10 +15,4 @@ VENV_BIN=${VENV_PATH}/bin
 
 cd letsencrypt
 ./tools/venv.sh
-PYVER=`python --version 2>&1 | cut -d" " -f 2 | cut -d. -f1,2 | sed 's/\.//'`
-
-if [ $PYVER -eq 26 ] ; then
-    venv/bin/tox -e py26
-else
-    venv/bin/tox -e py27
-fi
+venv/bin/tox -e py27