Upgrade to WMCore version that supports both Py2 and Py3

[klannon]

Lobster uses an ANCIENT version of WMCore. Upgrade it to use the most recent version that is compatible with both Py2 and Py3. I expect that there will be a number of errors introduced by the WMCore version update that will need to be addressed because in the past, when we accidentally installed a more modern Py2 WMCore version, it broke many, many things.

[amaltaro]

I would suggest to try the latest WMCore release supporting both Py2 and Py3, which is:
https://github.com/dmwm/WMCore/releases/tag/1.5.7.patch1

If things don't go as expected and we want to downgrade it to the very first stable version support Py2 and Py3, then we can try:
https://github.com/dmwm/WMCore/releases/tag/1.5.3