Merge pull request juju#1069 from cderici/fix-make-test-target

juju#1069

#### Description

Tests run the linter before running .tox which crashes because tox wants to see the lint environment already generated. This swaps the operations so .tox target is run first to make sure the environments are generated before running anything.

Makefile

@@ -20,11 +20,11 @@ client:
 	$(PY) -m juju.client.facade -s "juju/client/schemas*" -o juju/client/
 
 .PHONY: run-unit-tests
-run-unit-tests: lint .tox
+run-unit-tests: .tox lint
 	tox -e py3
 
 .PHONY: run-integration-tests
-run-integration-tests: lint .tox
+run-integration-tests: .tox lint
 	tox -e integration
 
 .PHONY: run-all-tests