[SP-981] Backport of [BISERVER-10816] - Analysis datasource accessible via XMLA even when EnableXmla=false

The check for whether EnableXmla was set to false had a fixed string comparison, which used a different case and quote expectation than what was coming through.
Modified to allow single, double, or no quotes, and case insensitive.

This change also includes a cherry pick of a change to SecurityHelper (c6116a3) that was done on master which allowed setting a mock.  Required by PentahoXmlaServletTest.