SHDP-201 SHDP-202 SHDP-203 SHDP-204 SHDP-180 First changes for resource ...

...loader overhaul

Overhauling concepts around hdfs resource loader.
- Removed ChainedResourceLoader and modified HdfsResourceLoader to
extend DefaultResourceLoader. This allows to fall back to normal resource
resolving behaviour.
- New namespace handler for resource-loader-registrar which creates
bean for CustomResourceLoaderRegistrar.
- HadoopResourceLoaderParser is now parsing user attribute
- Added tests for namespace and other functional changes for
this commit.
- Tidy up, fixed some warning, javadocs, etc.