Tests now passing again.
Merge remote-tracking branch 'refs/remotes/origin/master' into leadership-integration-tests

Conflicts:
	cmd/jujud/agent/agent.go
	cmd/jujud/machine_test.go
Version detection for CentOS 7

* Detect when runing on CentOS 7
* This commit also makes all tests pass on CentOS
Move environment get/set/unset into a subcommand.
Fix up command registration.
First changed tests due to new gopkg.in/yaml.v1 version.
Merge branch 'master' of https://github.com/juju-actions/juju into fix-yaml-v1-tests
separate metrics code/tests; move helpers from uniter_test to util_test
drop uniter_old_test, move components into uniter_test and util_test as appropriate
Fixes after review.
remove extra quotes
Remove unneeded imports.
Merge branch 'master' of https://github.com/juju-actions/juju into fix-yaml-v1-tests
Split into text, YAML and JSON tests and used the new checkers.
Merge branch 'master' of https://github.com/juju/juju into fix-yaml-v1-tests
Rename network.BasicInfo as SubnetInfo
Skeleton Subnets method
Comment about maas Subnets
testing: Update MakeEnvironment to take CofingAttrs

Update the testing factory function MakeEnvironment to take a new parameter: ConfigAttrs. ConfigAttrs is a map of environment configuration attributes which override the factory defaults.
Fixed newline in test data.