This allows to solve the recurrent docker login issue by passing the
credentials to kubernetes as a secret.
Indeed docker login credentials are valid for 3 months then it is over.
We just need to pass the `ctareg` service account credentials in the
`ctaregsecrets` and we are done.
In addition `imagePullSecrets` works at the full cluster level as each
kubelet needs the registry credentials to pull its own image.
If `ctaregsecret` secret does not exists, kubernetes is perfectly fine
with that and uses the default authentication. This means that there is
no need to define this secret (which is useless in the buildtree
environment).

Fixed home directory not readable (prevented the frontend from running).
Added installation of CASTOR's rmcd to the image.

Using lower case only for configmap keys as Eric had a problem with upper case with the same kubectl binary... Will be fine for everyone this way.