Dropping lower constraints testing and remove py36,py37 support

We facing errors related to the new pip resolver, this
topic was discussed on the ML and QA team proposed to
to test lower-constraints [1].

I propose to drop this test because the complexity and recurring pain needed
to maintain that now exceeds the benefits provided by this mechanismes.

[1] http://lists.openstack.org/pipermail/openstack-discuss/2020-December/019390.html

Change-Id: I60f1f739f25755cd344fe45e76d225712fedc40f

.zuul.yaml

@@ -1,8 +1,7 @@
 - project:
     templates:
       - openstack-cover-jobs
-      - openstack-lower-constraints-jobs
-      - openstack-python3-wallaby-jobs
+      - openstack-python3-zed-jobs
       - publish-openstack-docs-pti
       - check-requirements
       - release-notes-jobs-python3

lower-constraints.txt

@@ -1,71 +0,0 @@
-appdirs==1.3.0
-asn1crypto==0.23.0
-cffi==1.14.0
-cliff==2.8.0
-cmd2==0.8.0
-coverage==4.0
-cryptography==2.7
-debtcollector==1.2.0
-decorator==4.4.0
-deprecation==1.0
-dogpile.cache==0.8.0
-extras==1.0.0
-fixtures==3.0.0
-future==0.16.0
-idna==2.6
-iso8601==0.1.11
-jmespath==0.9.0
-jsonpatch==1.16
-jsonpointer==1.13
-jsonschema==2.6.0
-keystoneauth1==3.4.0
-linecache2==1.0.0
-mccabe==0.2.1
-monotonic==0.6
-mox3==0.20.0
-msgpack-python==0.4.0
-munch==2.1.0
-netaddr==0.7.18
-netifaces==0.10.4
-openstacksdk==0.36.0
-os-client-config==1.28.0
-os-service-types==1.2.0
-osc-lib==2.0.0
-oslo.config==5.2.0
-oslo.context==2.19.2
-oslo.i18n==3.15.3
-oslo.log==3.36.0
-oslo.serialization==2.18.0
-oslo.utils==3.33.0
-oslotest==3.2.0
-pbr==2.0.0
-positional==1.2.1
-prettytable==0.7.2
-pycparser==2.18
-pyinotify==0.9.6
-pyOpenSSL==17.1.0
-pyparsing==2.1.0
-pyperclip==1.5.27
-python-cinderclient==3.3.0
-python-dateutil==2.5.3
-python-glanceclient==2.8.0
-python-keystoneclient==3.8.0
-python-mimeparse==1.6.0
-python-novaclient==9.1.0
-python-openstackclient==5.2.0
-python-subunit==1.0.0
-pytz==2013.6
-PyYAML==3.13
-requests==2.14.2
-requests-mock==1.2.0
-requestsexceptions==1.2.0
-rfc3986==0.3.1
-simplejson==3.5.1
-six==1.10.0
-stestr==1.0.0
-stevedore==1.20.0
-testtools==2.2.0
-traceback2==1.4.0
-unittest2==1.1.0
-warlock==1.2.0
-wrapt==1.7.0

setup.cfg

@@ -7,7 +7,7 @@ license = Apache License, Version 2.0
 author = OpenStack
 author-email = openstack-discuss@lists.openstack.org
 home-page = https://docs.openstack.org/python-saharaclient/latest/
-python-requires = >=3.6
+python-requires = >=3.8
 classifier =
     Environment :: OpenStack
     Intended Audience :: Information Technology
@@ -18,9 +18,8 @@ classifier =
     Programming Language :: Python :: Implementation :: CPython
     Programming Language :: Python :: 3 :: Only
     Programming Language :: Python :: 3
-    Programming Language :: Python :: 3.6
-    Programming Language :: Python :: 3.7
     Programming Language :: Python :: 3.8
+    Programming Language :: Python :: 3.9
 
 [files]
 packages =

tox.ini

@@ -93,9 +93,3 @@ extension =
     S375 = checks:use_jsonutils
     S360 = checks:no_mutable_default_args
 paths = ./saharaclient/tests/hacking
-
-[testenv:lower-constraints]
-deps =
-  -c{toxinidir}/lower-constraints.txt
-  -r{toxinidir}/test-requirements.txt
-  -r{toxinidir}/requirements.txt