Add EC2-specific config files to standalone/configuration

https://issues.jboss.org/browse/WFLY-1190

I have added configuration suitable for use inside the EC2 as well I've modified test suite so it is possible to run clustering tests with the EC2 configuration.
Actually I see 2 tests failing when running against the EC2:
org.jboss.as.test.clustering.cluster.ejb3.xpc.StatefulWithXPCFailoverTestCase(SYNC-tcp).testBasicXPC 
org.jboss.as.test.clustering.xsite.XSiteSimpleTestCase.testPutToBackupNotRelayed 

I will look at them anyways but I would like to know if the changes so far look good and can be merged. Since running test suite with standard configuration files works 100% I think it makes more sense to have base ec2 support merged or at least the approach to be accepted before putting more effort into it.