Fix config group for cinder multi_backend

This commit just updates the config group for the multi_backend option.
Tempest change d5c9602b created a volume-feature-enabled group and moved this
volume there but devstack was never updated with the change.

Closes-Bug: #1276326

Change-Id: Icf2e96783feec4edbd4d477f8492651cd9bb3f01
Move ironic to plugin

Also adds an is_ironic_enabled() function to prepare for an upcoming
change in is_service_enabled().

Change-Id: I6e6e0e8b70221e231785ab27e9b5d4836933ac4c
Make neutron tempest run with tenant isolation by default

This commit removes the workaround that switched tempest tenant isolation
to false if Neutron was enabled. Recent changes to both neutron and tempest
should make this safe finally.

Change-Id: I929fcc73a7ef9a10f01af422ff62f9d451d52ae3
remove database init from horizon

horizon default config no longer uses a session database, it uses
signed cookies instead, so we can stop doing db initialization and
cleanup (which based on errexit we weren't doing correctly anyway).

Change-Id: Icae4318e2784486db2888cbf353e95ac9a5d7cba
Merge "Fix config group for cinder multi_backend"
Merge "Move ironic to plugin"
Merge "remove database init from horizon"
Merge "Make neutron tempest run with tenant isolation by default"
Merge branch 'master' of https://github.com/openstack-dev/devstack