On fork, the tempfile module's pseudo random generator is
not reset. If several processes (e.g. two children or parent
and child) try to create a temporary file, they'll conflict.
This function can be used to reset the name generator which
contains the pseudo random generator.

A unittest is included. It is in a separate script because
it changes a variable in the tempfile module to speed up the
test.

Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>