Set jdt.core.tests.builder.mockcompiler packaging to eclipse-test-plugin

Contributes to
- eclipse-platform/eclipse.platform.releng.aggregator#3784

Author: HannesWell

org.eclipse.jdt.core.tests.builder.mockcompiler/pom.xml

@@ -21,5 +21,5 @@
   </parent>
   <artifactId>org.eclipse.jdt.core.tests.builder.mockcompiler</artifactId>
   <version>1.0.200-SNAPSHOT</version>
-  <packaging>eclipse-plugin</packaging>
+  <packaging>eclipse-test-plugin</packaging>
 </project>