[WFLY-490] domain tests are passing JVM arguments to servers just like integration tests

Small change to domain tests infrastructure so that the JVM arguments from the testsuite POM are passed to the servers, just like in integration tests. Few notes:

- I'm marking this as `WFLY-490` because my ultimate goal with this is to run the RBAC domain tests under security manager (which is now possible, with this commit).
- This might have some unforeseen consequences, not sure. I only know about a single difference: default memory configuration of the newly spawned servers used to be `-Xmx512m -XX:MaxPermSize=128m`, but with this change, it becomes `-Xmx512m -XX:MaxPermSize=256m` (see `testsuite/pom.xml`, line 148, `surefire.memory.args`).

Comments welcome.