New TurnKey Ansible version (15.1)

Update Ansible to latest upstream version - 2.7.10.
Switch to Python3 build of Ansible (previous releases used py2 build) - closes #1300. [ Stefan Davis ]
Include boto3 (AWS python library - python3 version) OOTB - closes #1301. [ Stefan Davis ]
Include Debian 'python3-pyfits' package. Not directly required but includes a working weakref.py file. The Python3 version in Stretch is buggy - see Debian bug #918716. Closes #1324. Issue #1325 tracks the future removal of the unrequired dependency at some point in the future.