1. start a process instance which contains an async start event via FormService#submitStartForm()

-> the variables are not persisted

AT:

• variables set during the start of a process with an async start event are persisted

See failing testcase:
https://github.com/camunda/camunda-bpm-platform/commit/7af4df9d26160952fd04168f6eebfbf328d66ae3#diff-01b7110b4b9b69e80138d60821281a40R217

Remarks regarding the solution:

• for non-async start event, variables and history should be set correctly
• for async start event, variables and history should have the correct entries with the restriction that activityInstanceId misses on HistoricFormPropertyUpdates. This is due to the problem that these updates have to be written before the async continuation at which the activityInstanceId is unknown yet. This drawback should be documented by a failing testcase and a corresponding ticket.