Declare support for Python3.8

Replace our tox-py36 job with tox-py38, extend the list of trove
classifiers for Python versions in package metadata, and replace the
"py35" in the tox.ini envlist with just "py3" so that folks running
`tox` unqualified on their systems will use whatever python3
interpreter they have on hand (odds are it's in our supported range
these days). Also uncap python-daemon so we use a version compatible
with Python >=3.8.

Change-Id: Ic464eefbd90ffaa2ef9079a23e7b15c167de3103

.zuul.yaml

@@ -332,7 +332,7 @@
         - tox-pep8
         - tox-py35:
             nodeset: ubuntu-xenial
-        - tox-py36
+        - tox-py38
         - nodepool-zuul-functional:
             voting: false
         - nodepool-functional-openstack:
@@ -355,7 +355,7 @@
         - tox-pep8
         - tox-py35:
             nodeset: ubuntu-xenial
-        - tox-py36
+        - tox-py38
         - nodepool-functional-openstack
         - nodepool-functional-openstack-src
         - nodepool-functional-k8s

requirements.txt

@@ -2,7 +2,7 @@ pbr>=1.3
 
 PyYAML
 paramiko>=2.0.1
-python-daemon>=2.0.4,<2.1.0
+python-daemon>=2.0.4
 extras
 statsd>=3.0
 PrettyTable>=0.6,<0.8

setup.cfg

@@ -15,6 +15,9 @@ classifier =
     Programming Language :: Python
     Programming Language :: Python :: 3
     Programming Language :: Python :: 3.5
+    Programming Language :: Python :: 3.6
+    Programming Language :: Python :: 3.7
+    Programming Language :: Python :: 3.8
 
 [pbr]
 warnerrors = True

tox.ini

@@ -1,7 +1,7 @@
 [tox]
 minversion = 3.1
 skipsdist = True
-envlist = pep8,py35
+envlist = pep8,py3
 ignore_basepython_conflict = True
 
 [testenv]