This is, I believe, the last non-htools specific file that still lived
in the htools directory; it's already widely used in non-htools code,
so let's move it before we add more functionality to this module.

All changes are related to the name change, imports fixup, etc.; there
are no other changes in this patch.

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