Return the same namedtuple that the future module returns

Instead of converting the namedtuple that the future wait
function returns into a normal tuple, just have our own
internal functions use the futures namedtuple directly instead
and avoid any conversion to/from that namedtuple into a normal
tuple.

Change-Id: I54b2595af8d58db60843195034d66a623c20277c
Merge "Return the same namedtuple that the future module returns"