Drop Django 1.11 support

Django 1.11 ends its extended support in April 2020 (which is before
Ussuri release), so horizon drops Django 1.11 support in Ussuri.

tox envs for non-primary Django versions are no longer needed in tox.ini
as testing environments for non-primary Django versions are setup in
the zuul jobs now.

horizon>=17.1.0 is required to use Django 2.2. requirements.txt and
lower-constraints.txt are updated accordingly. For more information,
please refer to [1]. This patch also removes py36 from tox.ini.

[1] https://etherpad.openstack.org/p/Enable_Django22_support_in_Horizon_Plugin

Change-Id: I9d0784d1a5b5c48414bb08600cae69002433c30b
Depends-On: https://review.opendev.org/#/c/700733/

lower-constraints.txt

@@ -10,11 +10,12 @@ django-appconf==1.0.2
 django-babel==0.6.2
 django-compressor==2.0
 django-pyscss==2.0.2
-Django==1.11
+Django==2.2
 extras==1.0.0
 fixtures==3.0.0
 flake8==2.5.5
 hacking==0.12.0
+horizon==17.1.0
 idna==2.6
 iso8601==0.1.12
 keystoneauth1==3.4.0

requirements.txt

@@ -9,4 +9,4 @@
 # PBR should always appear first
 pbr!=2.1.0,>=2.0.0 # Apache-2.0
 python-blazarclient>=1.0.1 # Apache-2.0
-horizon>=14.0.0.0b3  # Apache-2.0
+horizon>=17.1.0  # Apache-2.0

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = py36,py37,py3-{dj111,dj22},pep8
+envlist = py37,pep8
 minversion = 3.1.1
 skipsdist = True
 ignore_basepython_conflict = True
@@ -18,8 +18,6 @@ deps = -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/
        -r{toxinidir}/requirements.txt
        -r{toxinidir}/test-requirements.txt
 commands =
-  dj111: pip install django>=1.11,<2
-  dj22: pip install django>=2.2,<2.3
   python manage.py test {posargs} --settings=blazar_dashboard.test.settings
 
 [testenv:pep8]