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 is updated accordingly.
For more info. please refer [1], [2].

[1] https://review.opendev.org/#/c/700733/
[2] https://etherpad.openstack.org/p/Enable_Django22_support_in_Horizon_Plugin

Change-Id: I6f393b85306e514f9e00567dfd2b9940d6f26253

Author: manchandavishal

requirements.txt

@@ -5,5 +5,6 @@
 pbr!= 2.1.0,>=2.0.0
 Babel>=1.3
 python-cloudkittyclient>=0.5.0
+horizon>=17.1.0 # Apache-2.0
 XStatic-D3>=3.5.17.0
 XStatic-Rickshaw>=1.5

test-requirements.txt

@@ -2,10 +2,6 @@
 # of appearance. Changing the order has an impact on the overall integration
 # process, which may cause wedges in the gate later.
 hacking>=1.1.0,<1.2.0 # Apache-2.0
-
-# Require Horizon
--e git://github.com/openstack/horizon.git#egg=horizon
-
 coverage>=3.6
 python-subunit>=0.0.18
 oslotest>=1.10.0 # Apache-2.0

tox.ini

@@ -1,6 +1,6 @@
 [tox]
 minversion = 2.0
-envlist = py36,py37,py3-{dj111,dj22},pypy,pep8
+envlist = py36,py37,pep8
 skipsdist = True
 
 [testenv]
@@ -12,8 +12,6 @@ setenv =
 deps = -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
    stestr run --slowest {posargs}
 
 [testenv:pep8]