Python3 missing on some environments

RHEL:
Python 3 was introduced in Qt dev (5.10) by https://codereview.qt-project.org/#/c/190958/.
That commit was then cherry-picked into 5.6 without RHEL 7.2 changes, as 5.6 doesn't have RHEL 7.2. https://codereview.qt-project.org/#/c/200690/

Qt 5.6 got another commit (https://codereview.qt-project.org/#/c/179662/) bringing unneeded python (python 2) install scripts into RHEL 7.2. Those weren't needed, as 5.6 doesn't have RHEL 7.2. That commit was then merged to 5.9 where a mistake was done, and RHEL 7.2 python scripts were removed. This was fixed by (https://codereview.qt-project.org/#/c/203710/) bringing python 2 scripts back into 5.9.

At this point we have python 3 cherry-picked into RHEL 6.6 in Qt 5.6, but we have nothing enabling it for RHEL 7.2 anywhere. The fix was for bringing back Python 2 scripts in 5.9.

The commit removing "unneeded python 2 scripts" has been since merged to dev, but the fix hasn't. That 's why dev branch hasn't currently python 2 or python 3.

What we need to is enable python 3 in Qt 5.9 and merge that commit to 5.10 and dev.

Windows 8
When the initial commit was done to install Python 3 in Windows 8, it was done for a platform called windows 8. It was also cherry-picked to 5.6. However, another commit climbing up the branch ladder was already introduced in 5.6 renaming the Windows 8 platform to Windows 8.1. So, the scripts were put in the wrong folder. These are being fixed by https://codereview.qt-project.org/#/c/205152/