* charm-helpers sync for classic charms
* sync from release-tools
* switch to release-specific zosci functional tests
* run focal-ussuri as smoke tests
* remove trusty, xenial, and groovy metadata/tests
* drop py35 and add py39
Change-Id: I8f7e9ee598a5fc218ccd68f4af36ea323af08bbb
e0a38a6393