This is a spin-off from: ros2/ros2#55

We need a generic program which can be run and then remotely instructed to load and execute a node.

This program should probably:

• Allow configuration of the internal executor.
• Provide ROS Services for loading and running a node.

This is not really useful until we have the ability to make, find, and dynamically load nodes, see:

• Provide CMake infrastructure for creating a node #114
• make producer / consumer plugins in a shared library and load them with pluginlib demos#18

This is also blocked by decisions that need to be made in: #48