Training examples initialization script (rebased onto dev_5_0)



This is the same as gh-2561 but rebased onto dev_5_0.

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As part of the ongoin effort to unify/run the trainings examples, this PR adds a first version of a CLI script which populates a server with a training user/group and some example data. 
Together with this PR, the merge-integration job will be rewritten to:
- run the population script against the integration server to create data
- generate a `training_ice.config` file populated with the credentials/object ids

Then the training job should:
- consume the config file created by the integration job
- run the various example scripts using this configuration file

/cc @jburel

                    
Doh. Sorry for finding in a rebase, but shouldn't this be "USER_NAME" rather than "training_user" ? Might want to also have GROUP_NAME if you're adding a commit.