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

tox.ini

@@ -4,7 +4,7 @@
 
 [tox]
 skipsdist = true
-envlist = modification,py{26,33,34,35,36},cover,lint
+envlist = modification,py{34,35,36},cover,lint
 
 [base]
 # pip installs the requested packages in editable mode
@@ -14,25 +14,22 @@ pip_install = {toxinidir}/tools/pip_install_editable.sh
 # before the script moves on to the next package. All dependencies are pinned
 # to a specific version for increased stability for developers.
 install_and_test = {toxinidir}/tools/install_and_test.sh
-py26_packages =
+all_packages =
     acme[dev] \
     .[dev] \
     certbot-apache \
     certbot-dns-cloudflare \
+    certbot-dns-cloudxns \
     certbot-dns-digitalocean \
+    certbot-dns-dnsimple \
+    certbot-dns-dnsmadeeasy \
     certbot-dns-google \
+    certbot-dns-luadns \
+    certbot-dns-nsone \
     certbot-dns-rfc2136 \
     certbot-dns-route53 \
     certbot-nginx \
     letshelp-certbot
-non_py26_packages =
-    certbot-dns-cloudxns \
-    certbot-dns-dnsimple \
-    certbot-dns-dnsmadeeasy \
-    certbot-dns-luadns \
-    certbot-dns-nsone
-all_packages =
-    {[base]py26_packages} {[base]non_py26_packages}
 install_packages =
     {toxinidir}/tools/pip_install_editable.sh {[base]all_packages}
 source_paths =
@@ -54,32 +51,15 @@ source_paths =
     letshelp-certbot/letshelp_certbot
     tests/lock_test.py
 
-[testenv:py26]
-commands =
-    {[base]install_and_test} {[base]py26_packages}
-    python tests/lock_test.py
-deps =
-    setuptools==36.8.0
-    wheel==0.29.0
-passenv = TRAVIS
-
 [testenv]
 commands =
-    {[testenv:py26]commands}
-    {[base]install_and_test} {[base]non_py26_packages}
+    {[base]install_and_test} {[base]all_packages}
+    python tests/lock_test.py
 setenv =
     PYTHONPATH = {toxinidir}
     PYTHONHASHSEED = 0
 passenv =
-    {[testenv:py26]passenv}
-
-[testenv:py33]
-commands =
-    {[testenv]commands}
-deps =
-    wheel==0.29.0
-passenv =
-    {[testenv]passenv}
+    TRAVIS
 
 [testenv:py27-oldest]
 commands =
@@ -104,7 +84,6 @@ passenv =
     {[testenv]passenv}
 
 [testenv:lint]
-# recent versions of pylint do not support Python 2.6 (#97, #187)
 basepython = python2.7
 # separating into multiple invocations disables cross package
 # duplicate code checking; if one of the commands fails, others will