New option in HttpRetriver datasource

Issue: #715

The task involved:

Adding the option to disable the HttpRetriver when the remote server from which we retrieve data is not available.

We need this functionality because a datasource that can not connect to the server repeatedly (downloading data after http) creates a lot of events and unnecessary logs into the system.

How options stop in HttpRetriver works.

Examples:

1. The program attempts to connect and waits up to 30 seconds for the server to respond; when not connected, it turns off the data source, because the option stop is true.

      URL:  http://localhost:8080/greeting
      Timeout: 30 [s] 
      Retries: 0
      Stop: true
   

   Remote server is available but not responding:

   

   Remote server is not available:

   

2. The program attempts to connect and waits up to 30 seconds for the server to respond;
   and retries 3 times, when not connected, it turns off the data source, because the option stop is true.

   URL:  “http://localhost:8080/greeting”
   Timeout: 30 (s)
   Retries: 3
   Stop: true
   

   WARNING: When the program is trying to connect, so for approximately 90 sec. (3*30”), datasource cannot be switched off or updated.

   Resolve: To prevent this situation, set the timeout as little possible.

   Remote server is available but not responding:
   

   Remote server is not available:
   

Changes have been introduced to the released version 0.0.9.7

https://github.com/SCADA-LTS/Scada-LTS/releases

Pull request:

https://github.com/SCADA-LTS/Scada-LTS/pull/717