Use squid in from of slaptool to cache results.
Return stale values in case of overloaded haproxy.

Synchronous calculation are reactivated because performance should be improved
by new management of software installation.

It will reduce number of activities.

Introduce data caching and avoid re-doing modifications in case if no
important parameter changed.

As simulation and deliveries are less critical, run them less often in order
to give processing power to other tasks.

In order to do that, always use logger, and always in real time.
Logger is properly configured.
Then remove -c switch (kept in parameters but doesn't do anything).
Also factor code of whole slapos/grid directory about SlapPopen (now does the
log).

Conflicts:
	slapos/grid/slapgrid.py

The category is destination_section.

Software instance status does not depend anymore on Sale Packing List state.

Software release installation status does not depend anymore on Purchase
Packing List state.