clean up base Dockerfile

- run "yum update" after installing RDO repository (to ensure we get any
  package updates from this repository)
- "yum clean" after the "yum update" to prevent yum cache from being
  baked into the image

Change-Id: Id897fd85214855bb08f7e16da4bbdf07b821d991
Closes-Bug: 1379442

Previously, the glance-api start script would use the container
IP instead of the proxy IP for the public url when creating the
keystone endpoint. This causes keystone to provide an unreachable
IP within the public url and other OS services are unable to
connect to the public url.

Change-Id: I44befc84a90f59d535a951ee81aaff0fa1ba952d
Closes-Bug: 1379513

Previously the glance-base script did not configure the registry
host IP. This causes API to try connecting to registry on
localhost. Since registry is bound to MY_IP, api is unable to
connect to registry. This change adds support for the glance-base
script to configure the registry_host parameter in api.conf to
MY_IP.

Change-Id: I1c711ff8aa95abec5ca306f03bd7e0a3883ca578