IDE-1663 add tests for xml.search.ui plugin

- In eclipse,the tests run as a product "org.eclipse.platform.ide"
- In terminal, cd to ${liferay-ide-repo-location}/tools/tests/com.liferay.ide.xml.search.ui.tests/,
run "mvn verify".
- both of above, need to specify arg "-Dliferay.bundles.dir" where the sdks and portals for tests are stored
- finished PortletXmlVadationTests
- TODO, complete validation tests of other validators