Comment 2 for bug 1751564

My proposed solution for this would be for Horizon to check if the volume has the "multiattach" attribute set to True and compute API microversion 2.60 is available (which it can determine via compute API version discovery: https://developer.openstack.org/api-ref/compute/#list-all-major-versions ) - that it should then make the attach volume request with microversion 2.60, else it should give a user friendly error message that multiattach is not yet supported in compute.