Don't use ceph-devel on Fedora

Don't use ceph-devel on Fedora

A previous commit changed the spec to use librbd1-devel on
RHEL-7, since this replaces ceph-devel from RHEL-6:

  commit 6cfc8834c858849cc74c3082078dc91fb1cbae38
  Author: Peter Krempa <pkrempa@redhat.com>
  Date:   Thu Mar 5 11:40:54 2015 +0100

    spec: Enable RBD storage driver in RHEL-7

    Use correct package names too as they differ.

RHEL-7 inherited this rename from Fedora though, so it should
have also made Fedora use the new names.

This was missed, because Fedora still provides a (deprecated)
back-compat RPM for ceph-devel that just pulls in librbd1-devel
(and others).

Fixing this stops libvirt pulling Java into the build root in
Fedora.

Reviewed-by: Pavel Hrdina <phrdina@redhat.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>