Release sync for 20.08

- Classic charms: sync charm-helpers.
- Classic ceph based charms:  also sync charms.ceph
- Reactive charms: trigger a rebuild
- sync tox.ini
- sync requirements.txt and test-requirements.txt

func-test-pr: https://github.com/openstack-charmers/zaza-openstack-tests/pull/378
Change-Id: Ib075ccc228f9ac82ecc0c06c637b846dd6cc5187

rebuild

@@ -2,4 +2,4 @@
 # when dependencies of the charm change,
 # but nothing in the charm needs to.
 # simply change the uuid to something new
-5572890c-916b-4ec7-a77b-a9e9f53471ae
+d9cb6552-d02c-11ea-a90e-afd4456f0701

requirements.txt

@@ -5,4 +5,6 @@
 #
 # Build requirements
 charm-tools>=2.4.4
+# importlib-resources 1.1.0 removed Python 3.5 support
+importlib-resources<1.1.0
 simplejson

tox.ini

@@ -50,6 +50,11 @@ basepython = python3.7
 deps = -r{toxinidir}/test-requirements.txt
 commands = stestr run --slowest {posargs}
 
+[testenv:py38]
+basepython = python3.8
+deps = -r{toxinidir}/test-requirements.txt
+commands = stestr run --slowest {posargs}
+
 [testenv:pep8]
 basepython = python3
 deps = -r{toxinidir}/test-requirements.txt