[magnum] Use install deps script from DC/OS dir
[magnum] Use install deps script from DC/OS dir

Update DC/OS build job to use the install_imagebuild_deps from
DC/OS's DIB directory.

Change-Id: Ief8c51be3e466597bb5dd8a1e0f2fd42c1b270cc
Depends-On: I85c48d91ff0750d90358056a09287dfc1c12faf2

openstack-infra/project-config,openstack-infra/project-config