I think part of the problem is that there really is no way to bound CPU usage on virtual machines. The best you can do is monitor and kill VMs that over utilise the CPU.

When you ask for 0.5Cpu, you are given charts to show how much of the 0.5cpu you are using, but if you're running on a 4 core machine, you could be using 800% CPU and the VM will let you.

Mining is one of those use cases where you can put the VM in the naughty corner and shut it down, but when you spin it back up, they just go full pelt again.

I guess this is why you can mine on a VPS. If you buy bare metal, I'm sure you can do anything.