Incubator-superset: Test connection doesn't use DB_CONNECTION_MUTATOR

[thoralf-gutierrez]

Expected results

We use DB_CONNECTION_MUTATOR to modify some of the connect_args passed to the create_engine function, and I expect those modifications to be applied whenever connections are created.

Actual results

But unfortunately, the "Test Connection" button doesn't use DB_CONNECTION_MUTATOR, which mean the connections aren't set up properly and users get a pop up telling that the connection doesn't work, even though just clicking on "Save" would actually work.
See https://github.com/apache/incubator-superset/blob/master/superset/views/core.py#L1821-L1830

More context

We use DB_CONNECTION_MUTATOR to add additional user information to authenticate with the database.

Do you agree "Test Connection" should use DB_CONNECTION_MUTATOR? If yes, I can push a PR to fix it.

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[mistercrunch]

Good catch @thoralf-gutierrez, it seems like testconn should just instantiate a Database object and call get_sqla_engine

[thoralf-gutierrez]

Cool - I'll push a PR in the few next days.