Create managed config files yaml from config dir

Create managed config files yaml from config dir

This script requires ruamel.yaml to be installed in the environment that
it is run in

Will take a configuration tree and build up the JCasC managed files
section and output to stdout the resultant yaml

Expected configuration of the tree is as follows:

top
|- config_type
    |- file-id
        |- config-params.yaml
        |- content
        |- ??CredentialMappings.yaml
        |- ??CredentialMappings.sandbox.yaml
...

The ??CredentialMappins.yaml will be used for production systems and the
sandbox version for sandbox systems (pass a -s or --sandbox)

Change-Id: I196e99f1db40223a29e892eb86efd70ecaa328f0
Signed-off-by: Andrew Grimberg <agrimberg@linuxfoundation.org>