This option to install os-brick from git was only added
into lib/cinder previously. When testing all-in-one nodes
this worked fine, but if you have multi-node setups with
compute nodes that don't install any c-* services we
only get packaged os-brick. With this change non-cinder
nodes can now test against unreleased os-bricks.
Change-Id: Ibb7423d243d57852dada0b6298463bbdfc6dc63c