Move to modern asio interfaces
Move to modern asio interfaces

async_result is required to be able to support boost 1.70.  This commit
moves us to it.

Tested:
Compiled.  Changes are non-functional, and simply renamed in newer
versions of asio.

Change-Id: I46728dc146c4c49eff7907c6aa8bc1525eca5cc2
Signed-off-by: Ed Tanous <8bf3d0085830172833e6f5c916cff518b50f87b7@intel.com>

openbmc/sdbusplus,openbmc/sdbusplus,openbmc/sdbusplus,openbmc/sdbusplus