[Fix JENKINS-23017] delete the tmp workdir also

In order to not leave unlimited directories created by the polling cycle
in the tmp directory which results in reaching the system limit for
subdirectory numbers we should also delete the workdir itself and not ony its
contents.
Merge pull request #133 from uhausbrand/JENKINS-23017

[Fix JENKINS-23017] delete the tmp workdir also
Merge commit 'a04dcd9d7396dee31ef73a94f5e23d5f334c7c47' into HEAD