Output log message about task submission before we add callback. (#611)
Output log message about task submission before we add callback. (#611)

Previously:
In the case of a fast executed task, the task was complete by the
time we add the callback; in that case, the callback is executed
immediately, before the 'task launched' message.

This commit reverses that to give a more sensible looking log order.

Addresses part of #604.
swift-lang/swift-e-lab,Parsl/parsl,Parsl/parsl,Parsl/parsl,Parsl/parsl,swift-lang/swift-e-lab