Test 517 was sometimes failing because the command to reset the test
generates a focus event which was not being properly ignored.
Now the correct event should always be tested.
Make sure the command `move <direction>` properly sends the workspace
focus ipc event required for i3bar to be properly updated and redrawn.
Make `ipc_send_workspace_focus_event publicly available from ipc.h for
more flexible event sending.
Michael Stapelberg