adding support for baremetal hypervisor

New files for baremetal driver:
- lib/baremetal
- files/apts/baremetal

Adds two dependencies:
- google shell-in-a-box
- diskimage-builder

Enable by setting both:
  VIRT_DRIVER=baremetal
  ENABLED_SERVICES="$ENABLED_SERVICES,baremetal"

Change-Id: Ibf6fe1671a759a449c9eb0df47751d1b31ade591
diff --git a/stackrc b/stackrc
index 9e06028..49ccaa8 100644
--- a/stackrc
+++ b/stackrc
@@ -111,6 +111,10 @@
 RYU_REPO=https://github.com/osrg/ryu.git
 RYU_BRANCH=master
 
+# diskimage-builder
+BM_IMAGE_BUILD_REPO=https://github.com/stackforge/diskimage-builder.git
+BM_IMAGE_BUILD_BRANCH=master
+
 # Nova hypervisor configuration.  We default to libvirt with **kvm** but will
 # drop back to **qemu** if we are unable to load the kvm module.  ``stack.sh`` can
 # also install an **LXC** or **OpenVZ** based system.