Stop disabling the Neutron tempest plugin

The root cause for the Inspector grenade failures was an eventlet
monkey patch[1]. The issue now being solved, disabling the Neutron
tempest plugin is no longer necessary.

[1] https://review.openstack.org/#/c/399469/

Closes-bug: #1621791
Change-Id: Icaca019880054e1d89b81736c2815a222e8abc45
1 file changed