added block_device attribute
Merge branch 'master' of github.com:hashicorp/terraform into awsblockdevices
tests for aws instance block_device
Merge branch 'awsblockdevices' of github.com:buth/terraform into buth-awsblockdevices

Conflicts:
	builtin/providers/aws/resource_aws_instance.go
Merge branch 'buth-awsblockdevices'