Fix exception java.lang.StringIndexOutOfBoundsException from org.apache.commons.jexl.ExpressionImpl when running maven plugins:test-all

pom.siteDirectory mustn't be empty because in the maven-plugins root project we have : 
maven.site.stage.directory=/home/brett/public_html/maven-stage-site/${pom.siteDirectory.substring(22)}

git-svn-id: https://svn.apache.org/repos/asf/maven/maven-1/plugins/trunk@264656 13f79535-47bb-0310-9956-ffa450edef68

rar/src/plugin-test/project.xml

@@ -16,8 +16,6 @@
  * limitations under the License.
  */
  -->
-
-
 <project>
   <pomVersion>3</pomVersion>
   <name>Test project for Maven Rar Plugin</name>
@@ -34,7 +32,7 @@
   <url/>
   <issueTrackingUrl>http://bugzilla</issueTrackingUrl>
   <siteAddress>www.fooserver.org</siteAddress>
-  <siteDirectory/>
+  <siteDirectory>/www/maven.apache.org/reference/plugins/rar/</siteDirectory>
   <distributionDirectory/>
   <repository>
     <connection>scm:cvs:pserver:anoncvs@cvs.apache.org:/home/cvspublic:maven</connection>