WFLY-3727 Race condition during channel create vs start causing NPE on channel startup

Conflicts:
	clustering/infinispan/src/main/java/org/jboss/as/clustering/infinispan/subsystem/CacheContainerAddHandler.java
Merge pull request #6718 from rhusar/WFLY-3727_8x

[8.x] WFLY-3727 Race condition during channel create vs start causing NPE on c...