Will create the tempDirectory if it is missing.
this is useful if, for example, you switch the tmp directory from
webwork2/courses/courseName/html/tmp to something like
You don't want to create a courseName node for every course, you would
prefer to create only /ww/htdocs/tmp
the current version will create the node courseName if it doesn't exist
(or the name tmp in the first example) but will not create files
higher up the tree.