Make babel_extract_angular work with python 3

Also run pep8 env with python3 as pep8/flake8 python 3 is
generally more strict.

Change-Id: Id4669ca1f929826f07cfe2928092d0e7255fda6f
Closes-Bug: #1762992

horizon/utils/babel_extract_angular.py

@@ -15,6 +15,7 @@
 
 import re
 
+from oslo_utils import encodeutils
 from six.moves import html_parser
 
 
@@ -165,7 +166,7 @@ def extract_angular(fileobj, keywords, comment_tags, options):
     parser = AngularGettextHTMLParser()
 
     for line in fileobj:
-        parser.feed(line)
+        parser.feed(encodeutils.safe_decode(line))
 
     for string in parser.strings:
         yield(string)

tox.ini

@@ -46,6 +46,7 @@ commands =
     bash {toxinidir}/tools/unit_tests.sh {envpython} {toxinidir} {posargs}
 
 [testenv:pep8]
+basepython = python3
 # sphinx (precisely Pygments) needs to be installed to make doc8 work properly
 deps =
   {[testenv]deps}