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

Change-Id: I92d284b9307e68e9f1d81abdc4809213a46d89a8

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
-91f48bd2-a4d0-11ea-9b76-4f13d1e70c89
+da035a02-d02c-11ea-acd0-e33fd64973a3

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