Add support for python 3.8

Introduce support of python 3.8 [1] and move tox and jobs to py38.

jsonschema 3.2.0 [2] support python 3.8
pyOpenSSL 19.1.0 [3] support python 3.8

[1] https://governance.openstack.org/tc/reference/runtimes/victoria.html#python-runtimes-for-victoria
[2] python-jsonschema/jsonschema#627
[3] https://pypi.org/project/pyOpenSSL/19.1.0/

Change-Id: I8f561325780a95173501f42e10b6fce617bb17f4

Author: likui

lower-constraints.txt

@@ -22,7 +22,7 @@ Jinja2==2.10
 jmespath==0.9.0
 jsonpatch==1.16
 jsonpointer==1.13
-jsonschema==2.6.0
+jsonschema==3.2.0
 keystoneauth1==3.4.0
 linecache2==1.0.0
 MarkupSafe==1.0
@@ -46,7 +46,7 @@ positional==1.2.1
 prettytable==0.7.2
 pycparser==2.18
 Pygments==2.2.0
-pyOpenSSL==17.1.0
+pyOpenSSL==19.1.0
 pyparsing==2.1.0
 pyperclip==1.5.27
 python-cinderclient==3.3.0