[WFCORE-447] Add jboss-metadata-common 8.1.2.Final

This component is used by subsystem-tests/framework to resolve expressions in the
subsystem's XML prior to validate it against a XSD schema.

JIRA: https://issues.jboss.org/browse/WFCORE-447
Add XSD validation of susbsystem'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 activate the validation tests.
Add XSD validation of the IO subsystem's XML
Merge pull request #377 from jmesnil/xml_validation

Add XSD validation of subsystem's XML