Overcloud image building

Create initial directory for instack, and clone the needed repositories.

  mkdir instack
  cd instack
  git clone https://github.com/agroup/instack-undercloud

Setup needed checkouts. If you don't want to use Delorean packages, or the last known good commits (use latest from trunk), then set those environment variables to 0. Exporting RUN_INSTACK=0 will create the initial checkouts. Note however that some pip dependencies will still be installed on the machine.
```
 # If you don't want to use Delorean...
 # export DELOREAN=0
 # If you don't want to use the last known good commits...
 # export LKG=0

 source instack-undercloud/instack-sourcerc
 export RUN_INSTACK=0
 instack-install-undercloud-source
```
Run script to build images. This will create any Overcloud images and deployment images that don't already exist in the current directory. If you only need to rebuild a single image, make sure the other images already exist in the current directory.
```
 instack-build-images
```