provider/aws: Update paramter for DB Option Group

[catsby]

aws_db_option_group was recently added in #4401, however a test therein that was added to DB Instance used a presumably old parameter name option_group_name instead of just name, which caused said DB Instance test to fail.

This updates the test there and I made sure the existing DB Option group ones pass as well:

Running..

==> Checking that code complies with gofmt requirements...
/Users/clint/Projects/Go/bin/stringer
go generate $(go list ./... | grep -v /vendor/)
TF_ACC=1 go test ./builtin/providers/aws -v -run=TestAccAWSDBOptionGroup_ -timeout 120m
d=== RUN   TestAccAWSDBOptionGroup_basic
--- PASS: TestAccAWSDBOptionGroup_basic (9.43s)
=== RUN   TestAccAWSDBOptionGroup_sqlServerOptionsUpdate
--- PASS: TestAccAWSDBOptionGroup_sqlServerOptionsUpdate (18.16s)
=== RUN   TestAccAWSDBOptionGroup_multipleOptions
--- PASS: TestAccAWSDBOptionGroup_multipleOptions (11.39s)
PASS
ok      github.com/hashicorp/terraform/builtin/providers/aws    39.003s
Test:

[stack72]

Apologies for missing this! LGTM

[catsby]

No worries, you're still doing great work 😄

[ghost]

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