Merge ~adam-collard/maas-ci:system-tests-add-readme into ~maas-committers/maas-ci/+git/system-tests:master

[Adam Collard]

[systemtests] Add initial README

[Alberto Donato (ack)]

Nice!

review: Approve

diff --git a/README.md b/README.md
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+# MAAS System Tests
+
+MAAS System Tests are run using `tox` which in turn uses `pytest` to execute the tests.
+
+## Environment variables
+
+The behaviour of the tests can be configured using environment variables
+
+| Name                               | Description                                                                   |
+| ----------------                   | -----------                                                                   |
+| `MAAS_GIT_REPO`                    | Git repository to get MAAS from, defaults to `https://git.launchpad.net/maas` |
+| `MAAS_GIT_BRANCH`                  | Git branch to build MAAS from, defaults to `master`                           |
+| `MAAS_PPA`                         | PPA to get dependencies from, defaults to `ppa:maas-committers/latest-deps`   |
+| `MAAS_SYSTEMTESTS_BUILD_CONTAINER` | LXD container name to use for building MAAS, defaults to `maas-system-build`  |
+| `MAAS_SYSTEMTESTS_MAAS_CONTAINER`  | LXD container name to use for running MAAS, defaults to `maas-system-maas`    |
+
+
+## Containers
+
+The tests use two LXD containers:
+
+ * The build container
+ * The MAAS container
+
+As the name suggests, MAAS is built in the build container, and installed in the MAAS container.
+
+The MAAS container is bridged on to the networks defined in `config.yaml` which is needed to allow MAAS in the MAAS container to provide DHCP to the network.