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/keystone b/files/rpms/keystone
index ce41ee5..8b0953d 100644
--- a/files/rpms/keystone
+++ b/files/rpms/keystone
@@ -1,10 +1,10 @@
 MySQL-python
 python-greenlet
-libxslt-devel       # dist:f20
-python-lxml         #dist:f19,f20
-python-paste        #dist:f19,f20
-python-paste-deploy #dist:f19,f20
-python-paste-script #dist:f19,f20
+libxslt-devel       # dist:f20,f21
+python-lxml         #dist:f19,f20,f21
+python-paste        #dist:f19,f20,f21
+python-paste-deploy #dist:f19,f20,f21
+python-paste-script #dist:f19,f20,f21
 python-routes
 python-sqlalchemy
 python-webob