Allow to use Fedora 24 with devstack

Looks like f24 does not have any special change compared to the
previous release, we just need to add f24 where f23 present.

Change-Id: Ia4a58de4973ef228735c48b33453a0562dc65258
diff --git a/lib/ceph b/lib/ceph
index 3e0839a..e999647 100644
--- a/lib/ceph
+++ b/lib/ceph
@@ -116,7 +116,7 @@
 
 # check_os_support_ceph() - Check if the operating system provides a decent version of Ceph
 function check_os_support_ceph {
-    if [[ ! ${DISTRO} =~ (trusty|f22|f23) ]]; then
+    if [[ ! ${DISTRO} =~ (trusty|f22|f23|f24) ]]; then
         echo "WARNING: your distro $DISTRO does not provide (at least) the Firefly release. Please use Ubuntu Trusty or Fedora 20 (and higher)"
         if [[ "$FORCE_CEPH_INSTALL" != "yes" ]]; then
             die $LINENO "If you wish to install Ceph on this distribution anyway run with FORCE_CEPH_INSTALL=yes"