Testing nrpe relation does not work for focal-deployed controllers. The
test fails as the nrpe check generated is different on focal vs bionic
(focal uses snap.juju-db.daemon and bionic juju-db).
This commit adds checking of the inner controller series which allows
for different check paths and expected content.
Additionally, we add constraints to the outer machine for accommodating
the size of juju snaps/binaries.
Added a TEST_REPO_ROOT env var, which will be passed through by zaza,
for exposing the root directory of the repository. This allows us
to cleanly refer to the locally-prepped customized Ubuntu charm
required for functional testing.
Additionally, refactored overlays to reduce duplication, and added
a missing num_units setting needed for proper deployment.
juju-controller is deployed into the nested Juju environment living on
the ubuntu unit; it is not used in the parent environment at all, so it
should be removed.
