Using a different version for arquillian jboss containers

The `<version.org.jboss.as>` property has been upgraded to 7.4.0.Final, but the `org.jboss.as:jboss-as-arquillian-container-managed` dependency uses the same property. 

The problem is that there is no `org.jboss.as:jboss-as-arquillian-container-managed:7.4.0.Final` artifact (for 7.2.0.Final+, only internal *-redhat-x `org.jboss.as:jboss-as-arquillian-container-managed` artifacts are available)

This pull requests introduces a new property (`<version.org.jboss.as.arquillian>`) for use in the management of the `org.jboss.as:jboss-as-arquillian-container-managed` dependency. 

(Also, the `org.jboss.as:jboss-as-arquillian-container-managed:7.2.0.Final` has worked fine with all 7.2.0.Final+ containers (tested last with 7.4.0.Final-redhat-17, even.. )).