Improve command logs errors

[NicolasMahe]

Dependant of #771

The command logs was not returning error from the stream and the command was not even terminated.
So any error on the logs (like the service exists but doesn't run) was not displaying an nothing show up.

The err channel was not returned to the user and just discarded:

go func() {	
  <-errC	
  closer()	
}()

I also add to change something in chunker: https://github.com/mesg-foundation/core/pull/772/files#diff-f59c295c71a834c1b8615304341180e4
The function Close was blocking..

[antho1404]

Agree to merge this one when #771 is validated