vlan: add 'vlan_create_1000_bridges_over_1000_vlans' test
Try to add 1000 VLANs and 1000 bridges via libnm (2000 connection together, ipv4 and ipv6 disabled), then check connections and devices exist.
We cannot test performance directly, we need to run the test multiple times and then do some stats about running time (it should be running on 1.30, 1.32 and master, which should be enough data).