Curious… The one thing I can think of at the moment is related to the following:
Did you activate an update channel? I’m not sure on what version of Rockstor you are for the moment and I just want to make sure as the iso you are using installs 3.9.1-0, and activating the Testing channel, for instance, will bring you to 3.9.1-16. It’s still a very old version but that’s the version I’ve tested this workaround so it’s still worth making sure you’re at least on that version. Running yum info rockstor will give you that information reliably.
Speaking of Rockstor versions, I believe you were going to try building your Rockstor 4 installer; let us know how it went and if we can help with it. Rockstor 4 is the version to use at the moment, really, especially if we seem to have a hard time getting Rockstor 3 to work well for you.
I though it was the same, indeed… I was comparing the one above to the traceback in that post. I seem to be forgetting a post, unfortunately… 
Let us know if updating to Rockstor 3.9.1-16 makes a difference for you, it’s far fetched but it’s a simple thing to check so worth the try. If that still does not help, then we’ll try something else.
Cheers, and sorry I can’t seem to really grasp why this hack does not work here.