Description of problem:
Old VM created in F30 won't start anymore after upgrade from F30 to F31.


Version-Release number of selected component (if applicable):
virt-manager-2.2.1-2.fc31


How reproducible:
Upgrade to to F31 from F30.


Steps to Reproduce:
1. Start virt-manager
2. Run any of your old VM


Actual results:
Error starting domain: Error reading from "/sys/fs/cgroup/machine/cgroup.controllers": There is no such file or directory

Traceback (most recent call last):
   File "/usr/share/virt-manager/virtManager/asyncjob.py", line 75, in cb_wrapper
     callback (asyncjob, * args, ** kwargs)
   File "/usr/share/virt-manager/virtManager/asyncjob.py", line 111, in tmpcb
     callback (* args, ** kwargs)
   File "/usr/share/virt-manager/virtManager/object/libvirtobject.py", line 66, in newfn
     ret = fn (self, * args, ** kwargs)
   File "/usr/share/virt-manager/virtManager/object/domain.py", line 1279, in startup
     self._backend.create ()
   File "/usr/lib64/python3.7/site-packages/libvirt.py", line 1136, in create
     if ret == -1: raise libvirtError ('virDomainCreate () failed', dom = self)
libvirt.libvirtError: Error reading from "/sys/fs/cgroup/machine/cgroup.controllers": There is no such file or directory


Expected results:
Old VM starts and works.