Remove support for Fedora 21 (EOL); add F22 where appropriate

Fedora 21 reached its End Of Life (EOL) on 1-DEC-2015[1]; remove it as
supported distribution.

    - stack.sh: Remove Fedora 21 from list of supported distributions.
    - tools/fixup_stuff.sh: Make the minimum Fedora version to be F22 in
      from a conditional check in 'Python packages' section
    - files/rpms/general: Remove 'f21' from NOPRIME.
    - lib/ceph: Remove 'f21' from the check_os_support_ceph() function.
    - doc/source/index.rst: s/Fedora 21/Fedora 22/
    - pkg/elasticsearch.sh: Remove the 'if' conditional in the
      install_elasticsearch() function.

[1] https://fedoramagazine.org/fedora-21-end-life-december-1st/

Change-Id: Ifbcc3dd783ff2f362a464fbf4ca22f20cc2c658e
diff --git a/lib/ceph b/lib/ceph
index 4ac498a..3e0839a 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|f21|f22|f23) ]]; then
+    if [[ ! ${DISTRO} =~ (trusty|f22|f23) ]]; 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"