provider/aws: Fix crasher in Elastic Beanstalk Configuration with Options

[catsby]

ElasticBeanstalk Configurations will crash if you attempt to use option_settings with the following panic:

2016/03/20 22:17:08 [DEBUG] terraform-provider-aws: panic: interface conversion: interface {} is map[string]interface {}, not *schema.ResourceData
2016/03/20 22:17:08 [DEBUG] terraform-provider-aws: 
2016/03/20 22:17:08 [DEBUG] terraform-provider-aws: goroutine 85 [running]:
2016/03/20 22:17:08 [DEBUG] terraform-provider-aws: panic(0xe704e0, 0xc820129900)
2016/03/20 22:17:08 [DEBUG] terraform-provider-aws:     /usr/local/Cellar/go/1.6/libexec/src/runtime/panic.go:464 +0x3e6
2016/03/20 22:17:08 [DEBUG] terraform-provider-aws: github.com/hashicorp/terraform/builtin/providers/aws.optionSettingHash(0xae9880, 0xc8202c9a40, 0xc800000001)
2016/03/20 22:17:08 [DEBUG] terraform-provider-aws:     /private/tmp/terraform20160316-80855-hnqetc/terraform-0.6.13/src/github.com/hashicorp/terraform/builtin/providers/aws/resource_aws_elastic_beanstalk_configuration_template.go:229 +0x352

The issue is the optionSettingHash method trying to coerce the interface it receives into a * schema.ResourceData instead of the map[string]interface{} that it actually is.

Another issue that exists is that this resource has it's own implementation of option settings that differs from (but is meant to be identical to) Beanstalk Environments. (ref http://docs.aws.amazon.com/elasticbeanstalk/latest/api/API_CreateEnvironment.html and http://docs.aws.amazon.com/elasticbeanstalk/latest/api/API_CreateConfigurationTemplate.html).

This PR consolidates the implementations into the one used by Environment, and we also change the config option name from option_settings to match Beanstalk Environments setting, for consistency. These changes are backwards safe because any use of options_settings in the Configuration resource is currently crashing anyway.

This PR updates the code to be consistent and updates the documentation to match

Fixes #5741

[phinze]

LGTM

[ghost]

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