Create a single data structure for recipe metadata

[ahal]

There are a few global values that various things look for in a recipe. For example, RUN_CONTEXT, BROKEN, etc.

We should have a single construct for all recipe metadata. I guess for now we can keep using a global variable + dict:

META = {
    'disabled': 'true',
    'context': { ... },
}

Eventually we might want to move this to an external file and have that be the primary place to define a recipe, but for now we can leave them in the python module.