rados.py: correct some C types

trunc was getting size_t instead of uint64_t, leading to bad results
in 32-bit environments. Explicitly cast to the desired type
everywhere, so it's clear the correct type is being used.

Fixes: #5233
Signed-off-by: Josh Durgin <josh.durgin@inktank.com>
(cherry picked from commit 6dd7d469000144b499af84bda9b735710bb5cec3)
mon: fix preforker exit behavior behavior

In 3c5706163b72245768958155d767abf561e6d96d we made exit() not actually
exit so that the leak checking would behave for a non-forking case.
That is only needed for the normal exit case; every other case expects
exit() to actually terminate and not continue execution.

Instead, make a signal_exit() method that signals the parent (if any)
and then lets you return.  exit() goes back to it's usual behavior,
fixing the many other calls in main().

Backport: cuttlefish
Signed-off-by: Sage Weil <sage@inktank.com>
Reviewed-by: Joao Eduardo Luis <joao.luis@inktank.com>
(cherry picked from commit 92d085f7fd6224ffe5b7651c1f83b093f964b5cd)