Making getstatus_scan function name more accurate

[agrandville]

Getting functions are idempotents functions, such functions can be called several times and the result should be the same because they does not modify resources.
In class PatrowlEngine, calling getstatus_scan function will overwrite scan.status to FINISHED if all threads are ended.
It would be usefull to use this state to let engine forward errors to the manager console (eg: process missing, bad parameters,...)

ID	Severity	Message	Type	Timestamp
6753	ERROR	[EngineTasks/startscan_task/86a1aa2e-c087-4c20-bfb4-7e4df73c59ab] CheckStatus - response_status_code=200, response_status=ERROR, response_details=scan#208 options parsing failed ('unknown option', 'check_protocols'). Task failed.	ERROR	2020/06/18-09:14:26
6749	INFO	[EngineTasks/startscan_task/86a1aa2e-c087-4c20-bfb4-7e4df73c59ab] Engine 'TESTSSL01_ENGINE' has been selected.	INFO	2020/06/18-09:14:26
6748	INFO	[EngineTasks/startscan_task/86a1aa2e-c087-4c20-bfb4-7e4df73c59ab] Starting task...	INFO	2020/06/18-09:14:26

to avoid compatibility issue with current version, the only accepted return values are SCANNING or FINISHED, I proposed to just add a third state 'ERROR' and to add support for this state in PatrowlManager. Reason will be 'undefined' in this version.

A new branch, with a rewrite getstatus_scan who returns new stream like this one:

{
  "finished_at": 1592464466470,
  "reason": "scan#208 options parsing failed ('unknown option', 'check_protocols')",
  "status": "ERROR"
}

a new method updatestatus_scan who return same response and update scan status.