Fix wait query regression

shamefully introduced by myself in d61b659345385386ba8d3fff1158fe0923ae7ab8. 
(but there was no test case covering the missed thing :p)

and while at it : simplified and clarified handling of multiple components in a single request. (mostly DRY).

> And it was also needed because I used a super(klass, self) with the bad klass value..

damn, this makes the dbconn to be closed twice and the sqlite dbconn close method doesn't handle correctly multiple calls of itself.

This must be first merged in logstore-sqlite :  https://github.com/shinken-monitoring/mod-logstore-sqlite/pull/10