Add missing dbt commands

[dinigo]

According to the DBT CLI reference there are still some missing commands.

This solves:

• close #59 cause it implements DbtSourceOperator
• close #51 cause it implements DbtBuildOperator

[Gwildor]

I think the DbtRunOperationOperator requires a bit more work. It is, as far as I know, the only dbt command that takes a positional argument (the macro you want to run), and uses --args (why they don't use --vars like other commands I don't know) for passing extra flags to the operation (it's the only command I could find with that argument).

I got it working by doing something like this:

class DbtBaseOperator:

    @apply_defaults
    def __init__(self,
                 macro=None,
                 args=None,
                 *positional_args,
                 **kwargs):
        super(DbtBaseOperator, self).__init__(*positional_args, **kwargs)

        if args is not None and not isinstance(args, dict):
            raise AirflowException('The argument "args" should be a dictionary')

        self.macro = macro
        self.args = args

    def create_hook(self):
        self.hook = DbtHook(
            macro=self.macro,
            args=self.args)

        return self.hook

class DbtRunOperationOperator(DbtBaseOperator):
    @apply_defaults
    def __init__(self, profiles_dir=None, target=None, *args, **kwargs):
        super(DbtRunOperationOperator, self).__init__(profiles_dir=profiles_dir, target=target, *args, **kwargs)

    def execute(self, context):
        self.create_hook().execute('run-operation', self.macro)

And then of course adding the --args keyword in the hook as well. I don't run dbt locally, so I don't have an example patch for that.