add an explicit lifecycle id

This now allows to invoke the antrun plugin via
$> mvn antrun:run@enhance
diff --git a/openjpa-persistence-jdbc/pom.xml b/openjpa-persistence-jdbc/pom.xml
index ba1af43..de78d32 100644
--- a/openjpa-persistence-jdbc/pom.xml
+++ b/openjpa-persistence-jdbc/pom.xml
@@ -113,6 +113,7 @@
                 <artifactId>maven-antrun-plugin</artifactId>
                 <executions>
                     <execution>
+                        <id>enhance</id>
                         <phase>process-test-classes</phase>
                         <configuration>
                             <target>