introduction of detailed apis for centraldb

register_hypervisors, unregister_hypervisors, register_vms,
unregister_vms, update_vms, instead of generic "commit"

available as internal functions, but also as iqs
permissions fix
track hypervisor status and last seen date in centraldb

2 new columns : "last_seen" and "status"
"status" can be "online", "off" when swithed off properly, and
"unreachable" when timed out.
mode change
change way of counting timeout

The only storage of hypervisors last seen dates is now the database.
This is to solve a bug where we had a discrepancy after a timeout and
recovery.
fix error in test
introduction of the 2 functions to read centraldb

read_vms and read_hypervisors can be used internally, but only
read_hypervisors is used at the moment
iq_read_vms and iq_read_hypervisors can be used externally but nothing
uses these iqs yet
fix an error in ping mechanism

hypervisors with status "Off" are not pinged since they have been
deliberately switched off.
mutualize some functions of runarchipel and archipel-initinstall

to reduce code duplication between archipel-central-agent and
archipel-agent, we create 2 files initinstallutils and runutils in
archipel-core.
fix issues with previous commit

move more code to utils files
remove outdated modifications to runarchipel
cosmetic