Move reconnect logic to main thread

[jordeu]

Description

Has been reported some cases where Tower Agent after a long time running it gets stalled without reconnecting or sending the heartbeat anymore. It has been impossible to reproduce this scenario.

Trying to mitigate this problem this PR moves all the re-connection logic to the main thread.

[pditommaso]

Looking at the code I think the System.exit should only be used when there's a not recoverable error e.g. lack of the access token or when the expected work directory cannot be created.

Instead it looks to me there's a system exit even for transient errors e.g. timeout.

Even better, there should be classified in recoverable and not-recoverable with a corresponding exception. Recoverable error should be managed in the infinite while loop, instead the non-recoverable should be managed in the main method producing a system exit eg.

    public static void main(String[] args) {
      try { 
        PicocliRunner.run(Agent.class, args);
      } 
      catch( Throwable e ) {
         log.error("Some message ${e.message}", e)
         System.exit(1)
      }
    }