Add XSD validation of subsystem's XML

add methods in AbstractSubsystemBaseTest to validate the
subsystem's XML (either from the tests or from the templates
used to build the server configuration) against a given XSD schema

Subsystems need to override getSubsystemXsdPath() and
getSubsystemTemplates() to active the validation tests.

* validate IO susbystem's XML as an example
WF is on 8.1.1, with a PR to move to 8.1.2. Might as well be consistent. And will this cause any problems, as the general pattern is WFCORE controls the versions for its stuff.