wal-e v1 dropped support for Python 2

[carlosfunk]

I just did a fresh install and it failed due to using Python 2. The fix I've done for now is to pin the version of wal-e at 0.9.2, I'll submit a pull request for that soon. But we will also require a separate change in order to use the latest version of wal-e with Python 3.

failed: [dev] (item=wal-e) => {"cmd": "/usr/bin/pip install -U wal-e", "failed": true, "item": "wal-e", "msg": "stdout: Downloading/unpacking wal-e\n Running setup.py (path:/tmp/pip_build_root/wal-e/setup.py) egg_info for package wal-e\n Traceback (most recent call last):\n File \"<string>\", line 17, in <module>\n File \"/tmp/pip_build_root/wal-e/setup.py\", line 19, in <module>\n raise RuntimeError('Python versions < 3.4 are not supported.')\n RuntimeError: Python versions < 3.4 are not supported.\n Complete output from command python setup.py egg_info:\n Traceback (most recent call last):\n\n File \"<string>\", line 17, in <module>\n\n File \"/tmp/pip_build_root/wal-e/setup.py\", line 19, in <module>\n\n raise RuntimeError('Python versions < 3.4 are not supported.')\n\nRuntimeError: Python versions < 3.4 are not supported.\n\n----------------------------------------\nCleaning up...\nCommand python setup.py egg_info failed with error code 1 in /tmp/pip_build_root/wal-e\nStoring debug log for failure in /root/.pip/pip.log\n"}