[cw-ctl] use default `mkdtemp()` behaviour to store backup file internally
When using `mkdtemp(dir=instbkdir)`, a dedicated system user which hasn't the
permissions to write in /var/lib/cubicweb/instances/$INSTANCE/backup will not
be able to run the db-dump command.
debian/tmp/usr/lib/PY_VERSION/site-packages/cubicweb/common/ usr/lib/PY_VERSION/site-packages/cubicweb
debian/tmp/usr/lib/PY_VERSION/site-packages/cubicweb/entities/ usr/lib/PY_VERSION/site-packages/cubicweb
debian/tmp/usr/lib/PY_VERSION/site-packages/cubicweb/ext/ usr/lib/PY_VERSION/site-packages/cubicweb
debian/tmp/usr/share/cubicweb/cubes/ usr/share/cubicweb/
debian/tmp/usr/lib/PY_VERSION/site-packages/cubicweb/*.py usr/share/pyshared/cubicweb