we're using boost::outcome rather than leaf or stl types because stl
types are not available everywhere and leaf does not provide its own
storage for error values, relying on thread-locals and the stack. if
we want to use promises we won't have a stack and would have to wrap
everything into leaf-specific allocating wrappers, so outcome it is.
Change-Id: I35111a1f9ed517e7f12a839e2162b1ba6a993f8f
eldritch horrors
92eccfbd68