It was inconsistent to only set TMP and not TEMP / TEMPDIR. In the case
of slapos, it should be set by slapos node software

Most installation seem to cleanup tmp properly, so the use case cleaning
up seem not critical.

This TMP was also used to know what new files have been created, by
considering files newer that the creation date of this directory.
Compare the file dates with the creation of the source directory instead
( xxx__compile__ )