If plugin "network_segment_range" is not enabled and a new segment
is required, if no segmentation ID is provided in the request, the
segmentation ID assigned is randomly retrieved from the non
allocated segmentation IDs.
The goal is to improve the concurrent network (and segment) creation.
If several segments are created in parallel, this random query
will return a different segmentation ID to each one, avoiding the
database retry request.
Closes-Bug: #1920923
Conflicts:
neutron/common/utils.py
neutron/tests/unit/plugins/ml2/drivers/test_type_vlan.py
Change-Id: Id3f71611a00e69c4f22340ca4d05d95e4373cf69
(cherry picked from commit 6eaa6d83d7)
ab56a5cd65