Enh livestatus query: finish with empty line.

Mostly for consistency purpose : 
always send every request to Livestatus with a supplementary \n so that the query ends by an empty line (\n\n) which is the main condition that livestatus use to detect the end of a query packet/string.

See https://github.com/pynag/pynag/pull/173 for reference.
Agreed. 
I do that but that will also need me to adapt the tests accordingly i think. I could have that for next week at best ..