Fedora 20 will reach end of life on 23-JUN-2015[1]; remove it as
supported distribution. Add Fedora 22 where applicable.
- stack.sh: Remove Fedora 20 from list of supported distributions.
- files/rpms/general: Remove 'f20' from NOPRIME.
- lib/ceph: Remove 'f20' from the check_os_support_ceph()
function.
- doc/source/index.rst: s/Fedora 20/Fedora 21/
[1] https://lists.fedoraproject.org/pipermail/devel-announce/2015-May/001586.html
Change-Id: I8f2e1ddc24c071754b1cceb5bed5bdafdc9d9f79
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