GDA (8.34) Default ORBClass and ORBSingletonClass to the only classes we use.

Also make the default event channel name local.eventChannel and tidy up
the test cases.

This allows the gda.ORBClass, gda.ORBSingletonClass and gda.eventChannelName
properties to be removed from java.properties.
CORE: add script to load preferred version of Java
Revert "CORE: add script to load preferred version of Java"

This reverts commit b59497e293906c1817a35bde2ac0a5661738e5fe.

This script should be in dls-config instead.
Merge branch '8.34' of ssh://dascgitolite@dasc-git.diamond.ac.uk/gda/gda-core.git into 8.34