Migrate importer tests to the new tests infrastructure

Conflicts:

	src/extension/importer/rest/src/test/java/org/geoserver/importer/rest/RESTDataTest.java
	src/extension/importer/rest/src/test/java/org/geoserver/importer/rest/TaskResourceTest.java
Disabling these two tests untile they can be fixed properly
[GEOS-6304] Remove stax-api-1.0.1.jar from excel extension