Include a setNamespaceUri method, so that oslc-testsuite can implement
the TestManifest.

Would allow oslc-testsuite to run and execute a TestManifest that uses
its own NamespaceUri.  Still need to decide how to manage prefixes,
since oslc-testsuite does not use ldpt, but it will still load when
running the TestManifest.
Merge pull request #167 from ttsanton/master

Include a setNamespaceUri method, so that oslc-testsuite can implement the TestManifest.