When the property ENABLE_IDENTITY_V2 is set to
False in the local.conf file, devstack will:
* Disable the v2 API in Keystone paste config;
* Set Tempest to skip Identity v2 tests and use
v3 auth tokens to run all the other tests;
* Set Horizon to use v3 API and v3 auth tokens;
* Register the Identity endpoint as v3.
Change-Id: I2575a516244b848e5ed461e7f488c59edc41068d