chore(distro): check jdk version inside startup script(unix)
chore(engine-spring): java config in SpringProcessEngineTestCase

related to CAM-2646
fix(history): distinguish between events

-- also fixing some typos in method and variable names

Related to: #CAM-2365
chore(engine): make job executor hint configurable

- if configured, disables hints for exclusive jobs
- makes parallel execution of exclusive jobs less likely in cases where a
  job is a follow-up after an asynchronous signal was received
- timers that are due within the job executors wait time are nevertheless
  hinted at

related to CAM-2522
fix(engine): repair job lock state when setting retries

- reset the job lock when it has become inconsistent
- cases are:
  - retries are 0 but a lock is set (i.e. lock owner or expiration time)
  - a lock owner but no expiration time is set

related to CAM-2710