Revert "use default OID if missing in model"

discussed with Guillaum on IRC. This changes is to invasif for a
stable release.

This reverts commit dd327fcbc95ebc58a78d56760c7b1d3e016283f3.
Merge branch '2.3.x' of git+ssh://forge.fusioninventory.org/git/fusioninventory/agent into 2.3.x
Merge remote-tracking branch 'origin/2.3.x' into 2.3.x
switch default SNMP timeout to 5s
better changes description
Merge remote-tracking branch 'forge/2.3.x' into 2.3.x
Revert "switch default SNMP timeout to 5s"

This reverts commit d92724205e879415bbdeedddaf36e5979e6ebd55.

5s is known to create timeout with Juniper devices. We increase
the value to 15s.
ensure %setup is defined

this commit avoid some warning regarding undefined datadir.
use context-dependant SNMP default timeout

For discovery, keeping a low timeout is essential because every IP
adress will be probed one time for every set of credentials defined in
the query, and we don't have evidence sofar of false negatives.
For inventory, we assume the destination adress is an actual device.