Initial support for Fedora 21

Initial support for Fedora 21.  Add f21 to the distribution lists for
rpms, ensure "mariadb" is used over "mysqld" and enable it in the
distro check, as we have several reports of it working.

Tested with [1]

[1] http://download.fedoraproject.org/pub/fedora/linux/releases/test/21-Beta/Cloud/Images/x86_64/Fedora-Cloud-Base-20141029-21_Beta.x86_64.qcow2

Change-Id: I97cbede806e5c00363c7174fa1e9f286de96aab6
diff --git a/files/rpms/horizon b/files/rpms/horizon
index 7add23a..1d06ac2 100644
--- a/files/rpms/horizon
+++ b/files/rpms/horizon
@@ -12,8 +12,8 @@
 python-migrate
 python-mox
 python-nose
-python-paste        #dist:f19,f20
-python-paste-deploy #dist:f19,f20
+python-paste        #dist:f19,f20,f21
+python-paste-deploy #dist:f19,f20,f21
 python-routes
 python-sphinx
 python-sqlalchemy