Update multiattach tests

Multiattach tests use legacy format to create multiattach
volumes i.e. provide "multiattach=True" in request body of
a create volume operation.
This patch updates the multiattach tests to use multiattach
volume type, which is the standard and only way[1], to create
multiattach volumes.
Note that the old functionality will be changed by patch[2] and
passing multiattach=True in volume create request body will
error out with BadRequest.

Devstack will create the multiattach volume type, like an
operator will create in a real deployment, and set it as a
tempest config option (see depends on patch).

We are adding a new config option `volume_type_multiattach`
which is used as the multiattach volume type to create
multiattach volumes.

[1] https://docs.openstack.org/cinder/latest/admin/volume-multiattach.html#how-to-create-a-multiattach-volume
[2] https://review.opendev.org/c/openstack/cinder/+/874865

Depends-On: https://review.opendev.org/c/openstack/devstack/+/877337
Depends-On: https://review.opendev.org/c/openstack/devstack/+/877497
Depends-On: https://review.opendev.org/c/openstack/devstack/+/877548
Depends-On: https://review.opendev.org/c/openstack/devstack/+/877498
Depends-On: https://review.opendev.org/c/openstack/devstack/+/877499

Change-Id: I5f68ef56fcc55dfc636936dabb5e6ad761579519
4 files changed