LPS-45606 Add tomcat dependency, as it is not a dependency for the arquillian test support library.

cc/ @csierra First pull for testing plugins with arquillian. It requires these things: 1) having arquillian-support library (https://github.com/cgoncas/arquillian-support) dependency resolved, which builds a WebArchive with tests for the plugin being tested; 2) A configured running tomcat: with tomcat-manager installed, JMX enabled, and a user with admin rights over manager (please read this: https://github.com/liferay-labs/jira-metrics-portlet#testing); 3) the plugin being tested needs an arquillian.xml file with JMX configuration. This pull also includes some tests for calendar portlet