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/doc/source/index.rst b/doc/source/index.rst
index 2622436..4a1d93d 100644
--- a/doc/source/index.rst
+++ b/doc/source/index.rst
@@ -20,7 +20,7 @@
 
 #. Select a Linux Distribution
 
-   Only Ubuntu 14.04 (Trusty), Fedora 21 (or Fedora 22) and CentOS/RHEL
+   Only Ubuntu 14.04 (Trusty), Fedora 22 (or Fedora 23) and CentOS/RHEL
    7 are documented here. OpenStack also runs and is packaged on other
    flavors of Linux such as OpenSUSE and Debian.