[WFLY-3830] Use external-context for TIBCO EMS

Tibco EMS's JNDI provider is non-standard and accepts only CompoundName
in its lookup(Name) method while WildFly passes a CompositeName.

For such JNDI providers that accept only specific subtypes of Name, the
StringOnlyInitialContext will wrap a normal InitialContext and make sure
that any Name-based method is using the corresponding String-based
method (that is more likely to work as expected).

JIRA: https://issues.jboss.org/browse/WFLY-3830