Adding argLine into surefire plugin to pass in JVM args for tests.

Apparently, due to a bug in surefire, MAVEN_OPTS aren't sent when surefire forks a JVM for tests (read: http://www.bmchild.com/2012/04/permgen-out-of-memory-errors-on-maven.html). As a workaround, the suggested approach was to add <argLine> in the configuration.