az sql copy db does not support Serverless

## Describe the bug
az sql copy db does not seem to support Serverless.

If using --compute-model Serverless the command expects -e -f -c as parameters.
If -e GeneralPurpose is submitted the argument is unregonized. without -e it tries to create in Premium tier.

**Command Name**
`az sql db copy`

**Errors:**
```
az: error: unrecognized arguments: -e GeneralPurpose
```

## To Reproduce:
Steps to reproduce the behavior. Note that argument values have been redacted, as they may contain sensitive information.

- _Put any pre-requisite steps here..._
- `az sql db copy --compute-model Serverless -g {} -s {} --name {} --dest-resource-group {} --dest-name {} --dest-server {} -e {} -f {} -c {} --auto-pause-delay {}`

## Expected Behavior
DB-Copy is created.

## Environment Summary
```
Linux-4.15.0-1077-azure-x86_64-with-debian-stretch-sid
Python 3.6.5

azure-cli 2.2.0 *

```
## Additional Context
If using az db sql **create** the parameters work as expected.