Use engine as-is in SqlCreds.from_engine

[ispedals]

I was having similar issues as #23 where the connection string I used to create the SQLAlchemy engine was not in the format from_engine() expected.

However, is there a reason why from_engine() doesn't use the provided engine instance, like so?

def from_engine(cls, engine: sa.engine.base.Engine) -> "SqlCreds":
     sql_creds = cls.__new__(cls)
     sql_creds.engine=engine
     return engine

This prevents any assumptions from being broken, and other than for __repr__(), it doesn't appear the other class attributes are ever used.

[yehoshuadimarsky]

This is a very good point. Maybe we can change the engine to only require what it actually uses in the BCP command (server, database, username, password) and use duck typing for that, i.e. if it has those properties than we don't really care about what it is or anything else.

[vlasvlasvlas]

@ispedals can you make a fork with this change so we can test it? thanks!