Refactor tests to common parent folder to better code sharing (#2160)

Author: lresende

elyra/metadata/schemas/metadata-test.json

@@ -4,8 +4,8 @@
   "name": "metadata-test",
   "display_name": "Metadata Test",
   "namespace": "metadata-tests",
-  "metadata_class_name": "elyra.metadata.tests.test_utils.MockMetadataTest",
-  "schema_filter_class_name": "elyra.metadata.tests.test_utils.TestSchemaFilter",
+  "metadata_class_name": "elyra.tests.metadata.test_utils.MockMetadataTest",
+  "schema_filter_class_name": "elyra.tests.metadata.test_utils.TestSchemaFilter",
   "properties": {
     "schema_name": {
       "title": "Schema Name",

elyra/metadata/schemas/metadata-test2.json

@@ -4,7 +4,7 @@
   "name": "metadata-test2",
   "display_name": "Metadata Test2",
   "namespace": "metadata-tests",
-  "metadata_class_name": "elyra.metadata.tests.test_utils.MockMetadataTestRollback",
+  "metadata_class_name": "elyra.tests.metadata.test_utils.MockMetadataTestRollback",
   "properties": {
     "schema_name": {
       "title": "Schema Name",