spec: fix logic bug in deciding to turn on cgconfig

https://bugzilla.redhat.com/show_bug.cgi?id=738725

Commit ecd8725c tried to silence a spurious warning on the initial
libvirt install, and commit ba6cbb18 tried to fix up the logic to the
correct Fedora version, but the warning was still present due to a
logic bug: since %{fedora} and %{rhel} are never simulatanously
set, then 0%{rhel} <= 6 made the %if always true.  Checking for
minimum versions (via >=) is okay, but checking for maximum versions
(via <=) requires a prerequisite test that the platform being tested
is non-zero.

Also fix a bogus setting of with_libxl (although we previously
hard-code with_libxl to 0 for rhel earlier in the file, so this
was not as severe a bug).

* libvirt.spec.in (with_cgconfig): Don't enable cgconfig on F16.

libvirt.spec.in

@@ -147,7 +147,7 @@
 %endif
 
 # Fedora doesn't have new enough Xen for libxl until F16
-%if 0%{?fedora} < 16
+%if 0%{?fedora} && 0%{?fedora} < 16
 %define with_libxl 0
 %endif
 
@@ -948,7 +948,7 @@ fi
 %if %{with_cgconfig}
 # Starting with Fedora 16, systemd automounts all cgroups, and cgconfig is
 # no longer a necessary service.
-%if 0%{?fedora} <= 15 || 0%{?rhel} <= 6
+%if 0%{?rhel} || (0%{?fedora} && 0%{?fedora} < 16)
 if [ "$1" -eq "1" ]; then
 /sbin/chkconfig cgconfig on
 fi