Pipelines yml validator should be more strict

When running a pipeline with a step: that has an empty definition, pipelines will (correctly) error.

Pipelines suggests using the validator to vaildate the yml, but the validator finds no issues with it.

Ideally the validator would catch this.

The 'provision-prod-east' section in your bitbucket-pipelines.yml file is missing a 'step'.

Please add the missing 'step' to fix the error.