[server] extract "no pooler" CnxSet class to a _BaseCnxSet class
So we get rid of "if self._queue is None" in each method of _CnxSetPool
Also add helper get_cnxset(source, size) to instantiate the correct pooler class.
Document: cubicweb-doc
Title: CubicWeb Documentation
Author: Logilab
Abstract: Some base documentation for CubicWeb users and developers
Section: Programming
Format: HTML
Index: /usr/share/doc/python3-cubicweb-documentation/html/index.html
Files: /usr/share/doc/python3-cubicweb-documentation/html/*