rhel: user/group openvswitch does not exist

rhel: user/group openvswitch does not exist

Default ownership[1] for config files is failing on an empty system:
  Running scriptlet: openvswitch-2.9.0-3.fc28.x86_64
warning: user openvswitch does not exist - using root
warning: group openvswitch does not exist - using root
...

Required user/group need to be created in %pre as documented in
Fedora guideline[2]

[1] https://github.com/openvswitch/ovs/commit/951d79e638ecdb3b1dcd19df1adb2ff91fe61af8

[2] https://fedoraproject.org/wiki/Packaging:UsersAndGroups#Dynamic_allocation

Submitted-at: https://github.com/openvswitch/ovs/pull/223
Signed-off-by: Alan Pevec <alan.pevec@redhat.com>
Co-authored-by: Aaron Conole <aconole@redhat.com>
Signed-off-by: Aaron Conole <aconole@redhat.com>
Acked-by: Markos Chandras <mchandras@suse.de>
Signed-off-by: Russell Bryant <russell@ovn.org>