OK, my conclusion: I have to wait for AMD to deliver a driver for their hardware and will use nvidia until then. :/
Well, my conclusion is that you could also use "the old" Ubuntu 16.04 until you got a newer Ubuntu driver, or just run Windows until you could grab it, etc. Point being that "using nVidia" is only one possible alternative to rescue you from what seems to be your own personal intractable dilemma atm. OTOH, If you are being forced against your will to run Ubuntu 17 then that puts a different slant on things and you might consider calling the police and making a complaint?...Yes? (j/k!--There seem to be several posts of this melodramatic bent making the rounds lately...;))
Is there some reason you need the AMDGPU-PRO driver rather than the built-in driver that comes with 17.04 ? We push driver code directly upstream so it can be picked up by Linux distros, and Ubuntu 17.04 should include good driver support for the RX460 as installed. You can pick up newer kernels from the Ubuntu download sites which will give you newer/better support for Ryzen, and there are package repositories which will give you newer userspace drivers as well.
If you do need the AMDGPU-PRO driver for OpenCL or Vulkan, another option would be to install Ubuntu 16.04.2, which isn't really old in the sense that it includes the kernel and graphics stack from 16.10. In general though you will get better gaming & general desktop performance from the all-open stack that is integrated with Ubuntu 17.04, and you are going to want to pick up a newer kernel for best results from your Ryzen CPU anyways.
I need OpenCL. This is not included in the standard Ubuntu driver.
There seems to be a way to get all the packages into Ubuntu instead of using the AMDGPUpro. But this is a lilttle bit to complex for me, I am only a user, not an admin.
Ubuntu16 was no option, because at installation no hdd/ssd was detected - i could not install it. The driver for the Ryzen chipset or whatever was not included in the install DVD.
Now i know that i could have tried to use an old system from my FX-8350 or PhenomII and just start it, let it update a little bit and then with a little fortune the system would have been usuable.
I will give AMD another try if a VEGA32 and a driver for Ubuntu17 are available.
Still no driver for Ubuntu17.x available.
The RX460 is still in its box without being used.
The good thing is: it did not lose its worth due to the mining boom.
My hope is now Ubuntu 18 LTS.