available_features for Neutron tempest tests is default to "all" and
used from Victoria to enable/disable tests that has no API extension.
It is added here to make sure that stable gating will not execute these
tests (like for IPv6 metadata in neutron-tempest-plugin or updating
min_bw QoS values for port already attached to VMs)
Change-Id: Id1db503c8842477b0716fb75e953240f7982e74b
Related-Bug: #1882804