rpm: don't enable fuse on RHEL-6

Fuse was recently enabled whereever LXC is enabled:

  commit 34783a9e
  Author: Jiri Denemark <jdenemar@redhat.com>
  Date:   Fri Feb 9 13:42:50 2018 +0100

    spec: Enable fuse only if LXC is enabled

Unfortunately the version of Fuse in RHEL-6 is too old for libvirt's
needs, but we still have LXC enabled there.
Signed-off-by: NDaniel P. Berrangé <berrange@redhat.com>

libvirt.spec.in

@@ -167,7 +167,7 @@
 %endif
 
 # fuse is used to provide virtualized /proc for LXC
-%if %{with_lxc}
+%if %{with_lxc} && 0%{?rhel} != 6
     %define with_fuse      0%{!?_without_fuse:1}
 %endif