Fix MAGNUM_IMAGE_NAME setting
Fix MAGNUM_IMAGE_NAME setting

The exported setting is not available on the context of that execution.
Set that on the devstack/localrc file, together with MAGNUM_GUEST_IMAGE_URL,
to be picked up properly by the tests.

Change-Id: I22f616f7a9e2645cbf686ef02dd10ae726c9e674

openstack-infra/project-config,dongwenjuan/project-config,openstack-infra/project-config,Tesora/tesora-project-config,Tesora/tesora-project-config,dongwenjuan/project-config