Having a list of very targeted suppressions allows us to still run the
majority of tests with valgrind checking, and not fail when Rust does
some trickery. This is for example the case with `std::sync::Once`
which uses `num_procs` calling out to the cgroups subsystem, sometimes
with a null path.
Suggested-by: Rusty Russell <@rustyrussell>
Christian Decker