fix integration test : the root node of a PMD configuration is "ruleset" and not "resultset"

plugins/sonar-pmd-plugin/src/main/java/org/sonar/plugins/pmd/PmdProfileExporter.java

   }
 
   protected String exportPmdRulesetToXml(PmdRuleset pmdRuleset) {
-    Element eltRuleset = new Element("resultset");
+    Element eltRuleset = new Element("ruleset");
     for (PmdRule pmdRule : pmdRuleset.getPmdRules()) {
       Element eltRule = new Element("rule");
       addAttribute(eltRule, "ref", pmdRule.getRef());

plugins/sonar-pmd-plugin/src/test/java/org/sonar/plugins/pmd/PmdConfigurationTest.java

     assertThat(rulesets.size(), is(1));
     File xmlFile = new File(rulesets.get(0));
     assertThat(xmlFile.exists(), is(true));
-    assertThat(FileUtils.readFileToString(xmlFile), is("<?xml version=\"1.0\" encoding=\"UTF-8\"?>\r\n<resultset />\r\n\r\n"));
+    assertThat(FileUtils.readFileToString(xmlFile), is("<?xml version=\"1.0\" encoding=\"UTF-8\"?>\r\n<ruleset />\r\n\r\n"));
   }
 
   @Test

plugins/sonar-pmd-plugin/src/test/resources/org/sonar/plugins/pmd/export_simple.xml

 <?xml version="1.0" encoding="UTF-8"?>
-<resultset>
+<ruleset>
   <rule ref="rulesets/coupling.xml/CouplingBetweenObjects">
     <priority>2</priority>
     <properties>
   <rule ref="rulesets/design.xml/UseNotifyAllInsteadOfNotify">
     <priority>4</priority>
   </rule>
-</resultset>
+</ruleset>
 

plugins/sonar-pmd-plugin/src/test/resources/org/sonar/plugins/pmd/export_xpath_rules.xml

 <?xml version="1.0" encoding="UTF-8"?>
-<resultset>
+<ruleset>
   <rule class="net.sourceforge.pmd.rules.XPathRule" message="This is bad" name="MyOwnRule">
     <priority>3</priority>
     <properties>
       </property>
     </properties>
   </rule>
-</resultset>
+</ruleset>