spec: proper soft static allocation of qemu uid

spec: proper soft static allocation of qemu uid

https://bugzilla.redhat.com/show_bug.cgi?id=924501 tracks a
problem that occurs if uid 107 is already in use at the time
libvirt is first installed.  In response that problem, Fedora
packaging guidelines were recently updated.  This fixes the
spec file to comply with the new guidelines:
https://fedoraproject.org/wiki/Packaging:UsersAndGroups

* libvirt.spec.in (daemon): Follow updated Fedora guidelines.

Signed-off-by: Eric Blake <eblake@redhat.com>
(cherry picked from commit a2584d58f6f7d941b960f996c8e26df8294b79b9)