az functionapp identity assign does not honor role param

## Describe the bug

**Command Name**
`az functionapp identity assign `

**Errors:**

## 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 functionapp identity assign -g jongrg4 -n jongfuncblob2 --role b7e6dc6d-f1e8-4753-8033-0f276bb0955b`

## Expected Behavior

I expect that role to be assigned, but it is not.

Before run:

After run:

Click on "Show the Azure RBAC..." link

No role assignments:

> It works if I also include a scope, but I think they should be mutually exclusive.

## Environment Summary
```
Windows-10-10.0.18362-SP0
Python 3.6.6
Shell: cmd.exe

azure-cli 2.0.76 *

```
## Additional Context

azsdke2e