Update hacking for Python3

The repo is Python 3 now, so update hacking to version 3.0 which
supports Python 3.

Fix problems found.

Update local hacking checks for new flake8.

Remove hacking and friends from lower-constraints, they are not needed
to be installed at run-time.

Change-Id: Ia6af344ec8441dc98a0820176373dcff3a8c80d5

lower-constraints.txt

@@ -30,7 +30,6 @@ eventlet==0.20.0
 extras==1.0.0
 fasteners==0.14.1
 fixtures==3.0.0
-flake8==2.5.5
 freezegun==0.3.10
 future==0.16.0
 futurist==1.8.0
@@ -38,7 +37,6 @@ gitdb2==2.0.3
 GitPython==2.1.8
 gnocchiclient==7.0.1
 greenlet==0.4.13
-hacking==0.12.0
 idna==2.6
 imagesize==1.0.0
 iso8601==0.1.12
@@ -95,14 +93,12 @@ Paste==2.0.3
 PasteDeploy==1.5.2
 pbr==3.1.1
 pecan==1.3.2
-pep8==1.5.7
 pika==0.10.0
 pika-pool==0.1.3
 prettytable==0.7.2
 psutil==5.4.3
 pycadf==2.7.0
 pycparser==2.18
-pyflakes==0.8.1
 Pygments==2.2.0
 pyinotify==0.9.6
 pyOpenSSL==17.5.0