If you specify just a bare ID, then the initial application works but
subsequent applications may end up doing bad things, like:
```
-/+ aws_ebs_volume.vol_1
availability_zone: "us-east-1a" => "us-east-1a"
encrypted: "true" => "true"
iops: "" => "<computed>"
kms_key_id: "arn:aws:kms:us-east-1:123456789:key/59faf88b-0912-4cca-8b6c-bd107a6ba8c4" => "59faf88b-0912-4cca-8b6c-bd107a6ba8c4" (forces new resource)
size: "100" => "100"
snapshot_id: "" => "<computed>"
```
Some error-checking was omitted.
Specifically, the cloudTrailSetLogging call in the Create function was
ignoring the return and cloudTrailGetLoggingStatus could crash on a
nil-dereference during the return. Fixed both.
Fixed some needless casting in cloudTrailGetLoggingStatus.
Clarified error message in acceptance tests.
Removed needless option from example in docs.
The default for `enable_logging`, which defines whether CloudTrail
actually logs events was originally written as defaulting to `false`,
since that's how AWS creates trails.
`true` is likely a better default for Terraform users.
Changed the default and updated the docs.
Changed the acceptance tests to verify new default behavior.
George Christou