Set default branch for git review/gerrit.
Switch tests to stable.
Switch to using stable charm-helpers branch.
Switch to using stable charm.openstack branch.
Switch to using stable zaza branch.
Switch to using stable zaza-openstack-tests branch.
Also updates for testing period for 20.01 release.
All these changes are needed together in order to have passing
functional tests.
Includes updates to charmhelpers/charms.openstack for cert_utils
and unit-get for the install hook error on Juju 2.9
* charm-helpers sync for classic charms
* rebuild for reactive charms
* ensure tox.ini is from release-tools
* ensure requirements.txt files are from release-tools
* On reactive charms:
- ensure master branch for charms.openstack
- ensure master branch for charm-helpers