Moves a .h file added outside of the zephyr include folder to be
within the zephyr include folder.
Signed-off-by: Jamie McCrae <jamie.mccrae@nordicsemi.no>
Adds a simple mcumgr test which checks that the os_mgmt echo commmand
works and responds with the correct data.
Signed-off-by: Jamie McCrae <jamie.mccrae@nordicsemi.no>