sd-bus: make sure bus_map_all_properties() handle booleans right

sd-bus generally exposes bools as "int" instead of "bool" in the public API.
This is relevant when unmarshaling booleans, as the relevant functions expect
an int* pointer and no bool* pointer. Since sizeof(bool) is not necessarily the
same as sizeof(int) this is problematic and might result in memory corruption.

Let's fix this, and make sure bus_map_all_properties() handles booleans as
ints, as the rest of sd-bus, and make all users of it expect the right thing.