RDS option and param groups should count only custom, not default

[jantman]

Right now the usage information for RDS option and parameter groups (including cluster) is counting default ones too, not just custom. It should just count custom.

[jantman]

Default parameter groups have a name of "default." and a description of "Default parameter group for ".

Default cluster parameter groups have a name of "default." and a description of "Default cluster parameter group for ".

Default option groups have a name of "default:{engine}-{engine_version}", where engine_version has dots converted to dashes, and the engine name is a lower-cased, normalized string. Their description is "Default option group for {engine} {engine_version}" where engine is a lower-cased, normalized string but the version is the normal dot-separated one.

[jantman]

This has been merged to develop as of 19a2526