Updated doc links, added Gem build notes
Updated doc links to docs.cloudfoundry.com
Merge pull request #143 from jbayer/gem-instructions

Gem instructions added to README
[openstack_cpi] Add image properties

Add some image properties supported by the OpenStack ImagePropertiesFilter
scheduler filter.
Merge pull request #144 from cloudfoundry/openstack_xen

[openstack_cpi] Add image properties