Create version placeholder for Kubernetes

Change to simplify maintenance.

Signed-off-by: Ron Stone <ronald.stone@windriver.com>
Change-Id: Iec2902997ebf0db63daf90794d36d3814e87cacd

doc/source/shared/strings.txt

@@ -25,6 +25,11 @@
 .. |result| replace:: Results
 .. |eg| replace:: Example
 
+.. Common version numbers
+
+.. |kube-ver| replace:: 1.23
+
+
 .. File-level minitoc label. Used with .. contents:: directive, as in
 .. .. contents:: |minitoc|
 ..    :depth: 1