Add a missing cleanup test for the regression suite.
Add a missing cleanup test for the regression suite.

Commit 7e8e530679862c64e6d69cdc1fc6697c29b4f54b added a machine to
the tests but did not clean it up, so the test to delete the
corresponding rack failed.

quattor/aquilon,guillaume-philippon/aquilon,quattor/aquilon,guillaume-philippon/aquilon,stdweird/aquilon,stdweird/aquilon,stdweird/aquilon,quattor/aquilon,guillaume-philippon/aquilon