Test playbook using molecule (#67)

* Test cluster using molecule

* Fix detection of first control node

* Include --flannel-iface and --node-ip as k3s arguments

* Store logs of k3s-init.service as GitHub job artifacts

molecule/README.md

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+# Test suites for `k3s-ansible`
+
+This folder contains the [molecule](https://molecule.rtfd.io/)-based test setup for this playbook.
+
+## Scenarios
+
+We have these scenarios:
+
+- **default**:
+  A 3 control + 2 worker node cluster based very closely on the [sample inventory](../inventory/sample/).
+
+## How to execute
+
+To test on your local machine, follow these steps:
+
+### System requirements
+
+Make sure that the following software packages are available on your system:
+
+- [Python 3](https://www.python.org/downloads)
+- [Vagrant](https://www.vagrantup.com/downloads)
+- [VirtualBox](https://www.virtualbox.org/wiki/Downloads)
+
+### Set up VirtualBox networking on Linux and macOS
+
+_You can safely skip this if you are working on Windows._
+
+Furthermore, the test cluster uses the `192.168.30.0/24` subnet which is [not set up by VirtualBox automatically](https://www.virtualbox.org/manual/ch06.html#network_hostonly).
+To set the subnet up for use with VirtualBox, please make sure that `/etc/vbox/networks.conf` exists and that it contains this line:
+
+```
+* 192.168.30.0/24`
+```
+
+### Install Python dependencies
+
+You will get [Molecule, Ansible and a few extra dependencies](../requirements.txt) via [pip](https://pip.pypa.io/).
+Usually, it is advisable to work in a [virtual environment](https://docs.python.org/3/tutorial/venv.html) for this:
+
+```bash
+cd /path/to/k3s-ansible
+
+# Create a virtualenv at ".env". You only need to do this once.
+python3 -m venv .env
+
+# Activate the virtualenv for your current shell session.
+# If you start a new session, you will have to repeat this.
+source .env/bin/activate
+
+# Install the required packages into the virtualenv.
+# These remain installed across shell sessions.
+python3 -m pip install -r requirements.txt
+```
+
+### Run molecule
+
+With the virtual environment from the previous step active in your shell session, you can now use molecule to test the playbook.
+Interesting commands are:
+
+- `molecule create`: Create virtual machines for the test cluster nodes.
+- `molecule destroy`: Delete the virtual machines for the test cluster nodes.
+- `molecule converge`: Run the `site` playbook on the nodes of the test cluster.
+- `molecule side_effect`: Run the `reset` playbook on the nodes of the test cluster.
+- `molecule verify`: Verify that the cluster works correctly.
+- `molecule test`: The "all-in-one" sequence of steps that is executed in CI.
+  This includes the `create`, `converge`, `verify`, `side_effect` and `destroy` steps.
+  See [`molecule.yml`](default/molecule.yml) for more details.