test: fix the HTTPS over proxy test

The test was failing when libwww-perl really support HTTPS over
proxy.
See: https://github.com/libwww-perl/libwww-perl/pull/52
allow testing without models
allow testing without models
Add oid for vlan name
update expected results
Fix ifname in Mock SNMP
update expected results
use default if model doesn't bring any result
allow multiple default oids

and use another oid as first default for ifName
apply same strategy on generic properties

- fallback on default if model doesn't return any values
- allow multiple defaults
use multiple default OIDs for memory
add default values for serial number property
add default OID for MAC property
fix trunk ports identification
filter out bogus mac addresses
another default oid for serial number
reintroduce switch_vlan_context method

This seems to be needed, actually, and we know to implement it with
SNMPv3 now.
add reset_original_context() method
re-enable vlan-specific requests

This time, we use a better strategy: instead of blindly querying all
vlans, we just query vlans associated with ports without CDP/LLDP
informations.
switch to XML for models index

And get rid of FusionInventory::Test::Hardware