Make role compatible with Airflow 1.10.0

[jnogol]

Prerequisites

• Put an X between the brackets on this line if you have done all of the following:
  • Checked that your issue isn't already filled: https://github.com/issues?utf8=✓&q=is%3Aissue+user%3Aidealista
  • Checked that there is not already provided the described functionality

Description

Setting airflow_version to 1.10.0 and launching the playbook fails in the "Installing Airflow" task with the following output:

fatal: [airflow]: FAILED! => {"changed": false, "cmd": "/usr/bin/pip install --no-cache-dir apache-airflow==1.10.0", "msg": "stdout: Collecting apache-airflow==1.10.0\n  Downloading https://files.pythonhosted.org/packages/da/2a/6e9efcd40193850e2f636c7306eede2ff5607aa9f81ff9f7a151d9b13ff8/apache-airflow-1.10.0.tar.gz (4.3MB)\n    Complete output from command python setup.py egg_info:\n    Traceback (most recent call last):\n      File \"<string>\", line 1, in <module>\n      File \"/root/pip-build-u203T5/apache-airflow/setup.py\", line 393, in <module>\n        do_setup()\n      File \"/root/pip-build-u203T5/apache-airflow/setup.py\", line 258, in do_setup\n        verify_gpl_dependency()\n      File \"/root/pip-build-u203T5/apache-airflow/setup.py\", line 49, in verify_gpl_dependency\n        raise RuntimeError(\"By default one of Airflow's dependencies installs a GPL \"\n    RuntimeError: By default one of Airflow's dependencies installs a GPL dependency (unidecode). To avoid this dependency set SLUGIFY_USES_TEXT_UNIDECODE=yes in your environment when you install or upgrade Airflow. To force installing the GPL version set AIRFLOW_GPL_UNIDECODE\n    \n    ----------------------------------------\n\n:stderr: Command \"python setup.py egg_info\" failed with error code 1 in /root/pip-build-u203T5/apache-airflow/\n"}