WFLY-3189 - validation errors on schema 



The ejb schema fail to validate properly in eclipse. Setting of schemaLocation confuses the XML Catalogs. Setting schemaLocation when importing a namespace is also not portable unless the schema exists in the same folder.

This PR also adds a schema file jboss-ejb-clustering_1_0.xsd who's namespace is declared in an online jboss ejb3 example, but does not exist in any existing schema. If the example is intentional, a new schema (such as provided here) should be added to the release. If the example is out of date, this second commit should be rejected and the online example should be fixed.

@pferraro 

1) Is this PR ok with you in general? This "urn:clustering:1.0" seems to be coming from https://docs.jboss.org/author/display/WFLY8/jboss-ejb3.xml+Reference (and equivalent 7.1 / 7.2 / 9 docs). The namespace name seems a bit broad, but we already use urn:security in an equivalent fashion, so what the heck. :)

2) This uses type="xs:string" but this is a boolean. But perhaps string is the idea to allow for expressions.