Prepare the six and python 2.7 support dropping

With python 3 the input function is safe.
The six dropping will re-introduce the usage of the input function
and bandit checks will fails.

We drop python 2.7 support so we ignore the bandit check B322 [1] before
starting to drop six support.

[1] https://bandit.readthedocs.io/en/latest/blacklists/blacklist_calls.html#b322-input

Change-Id: Ie956a65ebc4c781c5e661e8021f674833be8b323

tox.ini

@@ -30,13 +30,14 @@ commands =
     # B110: Try, Except, Pass detected.
     # B310: Audit url open for permitted schemes
     # B311: Standard pseudo-random generators are not suitable for security/cryptographic purposes
+    # B322: The input method is safe in Python 3.
     # B404: Import of subprocess module
     # B410: Import of lxml module
     # B504: Test for SSL use with no version specified
     # B506: Test for use of yaml load
     # B603: Test for use of subprocess with shell equals true
     # B607: Test for starting a process with a partial path
-    bandit -r heat -x tests --skip B101,B104,B107,B110,B310,B311,B404,B410,B504,B506,B603,B607
+    bandit -r heat -x tests --skip B101,B104,B107,B110,B310,B311,B322,B404,B410,B504,B506,B603,B607
     doc8 {posargs}
 
 [testenv:venv]