SubstringMatchingRuleTest.java:
Added strings() + used it in all subclasses.

git-svn-id: https://svn.forgerock.org/opendj/trunk@11081 41b1ffd8-f28e-4786-ab96-9950f0a78031
Backport CR-4738 OPENDJ-1581: Cover disk space thresholds in the Admin Guide

git-svn-id: https://svn.forgerock.org/opendj/trunk@11084 41b1ffd8-f28e-4786-ab96-9950f0a78031