vtkWeb: Teach launcher.py to wait for ready_line

Rather than just waiting the full timeout check the output of the
process for the ready_line ( which is configured in launcher.json ).
This should resolve timing issues related to server websockets not
being ready to receive client connections. Also in error paths rather
than return status code 200 (ok) return a reasonable error code.

Change-Id: I3cd99ab5758184002500e3b9adc6208d0fd736e0
vtkWeb: Add appropriate error codes for launch requests

Rather than returning 200 ( ok ) set the response code to an
appropriate error code.

Change-Id: I5a474cb0ffd66881216d1600b51a1f560f5b2207
Merge topic 'vtkweb-launcher-ready-fix' into master

1d12532f vtkWeb: Add appropriate error codes for launch requests
9d81e15c vtkWeb: Teach launcher.py to wait for ready_line