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.
I understand your pov ;)

I think that without this I had a test failed and I may have concluded that this was the best thing to do..
I'll re-check about this later and then give feedback.