tests,python: Atomic directory creation

* lang/python/tests/Makefile.am:  Use MIDIR_P.
* tests/gpg/Makefile.am: Ditto.
* tests/gpgsm/Makefile.am: Ditto.

Solves race in parallel build when mkdir fails if directory exists.

• Tweaked the ChangeLog

• Signed-off-by: Werner Koch <wk@gnupg.org>