Fix clustering transformers and reenable in mixed-domain tests

When running the jgroups and infinispan subsystem tests with -Djboss.test.transformers.eap there are some failures in the transformers tests.

Also, in the mixed domain tests it is not possible to enable these subsystems, so I have removed them from DomainAdjuster620 in https://github.com/wildfly/wildfly/pull/7350. They should be reenabled again as part of this Jira.

Some info from private mail:

However, when transforming that to 7.2.0 by running:
mvn clean install -DallTests -Djboss.test.mixed.domain.dir=/Users/kabir/old-as7-releases/ -pl testsuite/mixed-domain/ -Dtest=MixedDomain_7_2_0_Final_TestSuite

I get the following error:
11:59:43,682 ERROR [org.jboss.as.host.controller] (Controller Boot Thread) JBAS010901: Could not connect to master. Aborting. Error was: java.io.IOException: 1-$-WFLYCTL0300: Transforming resource [
("profile" => "full-ha"),
("subsystem" => "infinispan"),
("cache-container" => "server"),
("transport" => "TRANSPORT")
] for host controller 'slave' to subsystem 'infinispan' model version '1.4.0' --there were problems with some of the attributes and this resource will need to be ignored on that host. Details of problems: [WFLYCLINF0027: Could not determine 'stack' attribute from JGroups subsystem]

I am not totally sure if this is the right solution, but I attempted to add a stack attribute to the transport, but it does not seem to get persisted so it goes away after reloading the DC (out of admin-only to normal mode). I also tried in standalone mode, and executing
/subsystem=infinispan/cache-container=server/transport=TRANSPORT:write-attribute(name=stack, value=udp)
and the stack does not get persisted.

It is probably a simple fix, but since I am not sure if it is the right fix or not, especially since adding this to the writer it also seems to be ignored by the parser. Perhaps this is a candidate for something along the lines of https://github.com/wildfly/wildfly/blob/master/clustering/jgroups/extension/src/main/java/org/jboss/as/clustering/jgroups/subsystem/ThreadsAttributesWriteHandler.java#L61 so that we can support old configs, but not actually use it on a server using the current version?

Note that the above is when I was working on this, the 7.2.0 test has been removed. We now test EAP 6.2.0 and 6.3.0 compatibility. I believe the problem is similar there although I have not dug in very deeply.