Add Redshift parameter to create tables with backup option specified

[dlb8685]

resolves #18

Description

This PR adds a config parameter "backup" that controls whether a Redshift table will be created with BACKUP No or not. Current default (both in DBT and more generally with Redshift) is for this BACKUP to be set to True unless explicitly overridden. But, for some transient and intermediate tables, there can be no need for backup and users would like to be able to set config accordingly.

The config parameter is added in impl.py and the statements in adapters.sql are updated to use this parameter.

Checklist

• I have signed the CLA
• I have run this code in development and it appears to resolve the stated issue
  I don't have a Redshift instance to run this code on. I will investigate if the unit tests fail, but based on nearly identical old PR and local linting I'm optimistic.
• This PR includes tests, or tests are not required/relevant for this PR
• I have updated the CHANGELOG.md and added information about my change to the "dbt-redshift next" section.

[dlb8685]

@jtcohen6 I was hoping the tests would run in CI to prove this out a bit, but I'm a first-time contributor. I don't have a Redshift database to do much with local testing. Let me know your thoughts in general and if there's anything that needs to be added.

[jtcohen6]

Closing and reopening to trigger adapter integration tests

[jtcohen6]

Thanks for reopening the PR here @dlb8685!

Looks like the tests are failing in a few small ways, should be quick to fix up. We're cutting a second (and last) RC of v1.0 very soon, so there's a good chance this goes into v1.1 instead, which is totally ok :)

[jtcohen6]

There aren't any seeds defined in the project

Suggested change

self.assertEqual(len(self.run_dbt(["seed"])), 1)

[jtcohen6]

Looks like this is causing an error in the integration test:

    def project_config_append(self, new_name, new_element):
>       self._project_config[new_name] = new_element
E       AttributeError: 'TestBackupTableOption' object has no attribute '_project_config'

Much simpler would be to create a separate test case, and define the config anew:

TestBackupTableOptionProjectFalse(TestBackupTableOption):

    @property
    def project_config(self):
        return {
            'config-version': 2,
            'models': {'backup': False}
        }

    @use_profile('redshift')
    def test__redshift_backup_table_option_project_config_false(self):
        ...

[dlb8685]

I made this change and also removed the lines that were running the seed. Let me know if this looks good and if the tests can run again.

[jtcohen6]

@dlb8685 Nice work! I think we might be able to sneak this in for v1.0.0rc2 after all :)

Just added you as a contributor in the changelog, will merge as soon as the tests pass.

[dlb8685]

Thank you! @jtcohen6

[will-peloton]

I reported a bug I think that is related to this #60. I believe the fix is moving backup option up 2 lines in the adapter.sql before setting dist_key.