Write Acceptance Test Harness for the External Workspace Manager plugin.

1. Test the Jenkins global config sections, External Workspace Definitions and External Workspace Templates. - e.g. fill in the text boxes, save, and verify if the information was saved correctly
2. Test the Node configuration, External Workspace property - select the checkbox and fill in the text boxes, after saving, the information should be persisted
3. Set-up a minimal config, with one node instance and create a basic pipeline job that runs the exwsAllocate and exws steps. Verify the console output for the logged messages. Verify if the External Workspaces run action outputs the appropriate information, e.g. selected disk pool, selected disk, complete path on disk.
4. Set-up a bit more complex environment, with two node instances. Maybe if I'll point the localRootPath parameter to the same path on both of the nodes, I may be able to test a bit more complex scenario, in which I will build the project on one node, and test the project on a different node.