* Add functions to retrieve the allowed and required parameters for boto3 client methods
* Add custom waiter for stopping an RDS DB instance
* Add rds_instance module
* Add rds_instance integration tests
* address requested changes from ryansb
* address requested changes from willthames
* address requested changes from dmsimard
* Fix final snapshots
Fix idempotence with already-deleting DB instances
Remove unused import from module_utils/aws/core.py
Consolidate function to get all boto3 client method parameters and the subset of required parameters
* Add some additional rds_instance integration tests
* Add some common functions to module_utils/aws/rds
* Move common code out of rds_instance
* Remove hardcoded engine choices and require the minimum boto3
* Document wait behavior
* Provide a list of valid engines in the error message if it is invalid
Add supported methods to whitelist
Remove AWSRetry around waiter
Wait for a less crazy amount of time
Remove unused variables
* Add a test for an invalid engine option
* pep8
* Missed adding a method to the whitelist
* Use retries
* Fix some little things
* Fix more things
* Improve error message
* Support creating cross-region read replicas
* Remove unused imports
* Add retry when getting RDS instance
* Soft-check required options so module fails properly when options are missing
* Fix mariadb parameter version
* Fix cross-region read_replica creation and tests
* fix modify tests
* Fix a modification test
* Fix typo
* Remove test for option_group_name that exists for this account but may not for others and added as a TODO to do properly
