The current directory is prepended to the rootFolder, which makes it impossible to use absolute paths. Only relative paths (../../workspace) will work.
I assume line 166 is the problem - but just testing things out so I did not want to try changing anything yet.
def rootFolder = (project.multiproject.rootFolder ? new File(project.projectDir, project.multiproject.rootFolder).canonicalFile : project.projectDir)
rootFolder '/tmp/workspace'
The current directory is prepended to the rootFolder, which makes it impossible to use absolute paths. Only relative paths (../../workspace) will work.
I assume line 166 is the problem - but just testing things out so I did not want to try changing anything yet.
def rootFolder = (project.multiproject.rootFolder ? new File(project.projectDir, project.multiproject.rootFolder).canonicalFile : project.projectDir)