Simplify late binding of runopts on instantiated Runnables

[randomir]

For example:

sa = hybrid.SimulatedAnnealingProblemSampler(sweeps=100)
...
sa.bind(sweeps=1000)
sa.partial(sweeps=1000)   # alternatively

would be a syntactic sugar for:

sa.next = functools.partial(sa.next, sweeps=1000)