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.
Can you move this code so the extra line break is added instead in LivestatusQuery.get_query() around line 2288 ?

We want the query to be correctly generated from the start, and push responsibility of calling livestatus correctly to the callers of write()

In the future this will mean that if we have to remove this extra line break (for example in case of a different livestatus engine) then we will not break backwards compatibility with callers of write().