rds_instance - add snapshot tests, update docs, refactor tests (ansib…

…le-collections#1081)

rds_instance - add snapshot tests, update docs, refactor tests

Depends-On: ansible-collections#776
Depends-On: ansible-collections#1105
SUMMARY

add snapshot tests to test restoring db from snapshot and fix bugs associated
fix some typos in documentation and remove duplicate parameter (added as alias so no breaking change)
remove unused IAM role in tests and add some missing cleanups

ISSUE TYPE

Bugfix Pull Request
Feature Pull Request

COMPONENT NAME
rds_instance
ADDITIONAL INFORMATION
this module had both db_snapshot_identifier and snapshot_identifier as separate params, with the latter being required to restore from snapshot, resulting in some parameter missing errors. moving snapshot_identifier as an alias of db_snapshot_identifier fixes this issue.

Reviewed-by: Alina Buzachis <None>
Reviewed-by: Joseph Torcasso <None>
Reviewed-by: Mark Chappell <None>
Reviewed-by: Sloane Hertel <None>

This commit was initially merged in https://github.com/ansible-collections/community.aws
See: ansible-collections/community.aws@5d5bca9

plugins/modules/rds_cluster.py

@@ -758,7 +758,7 @@ def get_rds_method_attribute_name(cluster):
             method_name = 'modify_db_cluster'
             method_options_name = 'get_modify_options'
         elif creation_source == 'snapshot':
-            method_name = 'restore_db_cluster_from_db_snapshot'
+            method_name = 'restore_db_cluster_from_snapshot'
             method_options_name = 'get_restore_snapshot_options'
         elif creation_source == 's3':
             method_name = 'restore_db_cluster_from_s3'