JENKINS-5077 created the ability to use custom workspaces in matrix jobs, however the implementation keeps the creation of a subtree specific to the axis and target (e.g. ${WORKSPACE}/axis1/a/axis2/b). This doesnt make sense some (most?) of the time as you're then not actually in the custom workspace you defined, but instead inside a subtree.

We need an option to disable this subtree creation so that all runs of a matrix job can share the root of a custom workspace.