az account management-group list only lists tenant root

_az account management-group list_ only lists the Tenant Root Group. It should have an option to work recursively like az account management show does.

Version: az

[Enter feedback here]
**Version details below:**
az --version
azure-cli 2.21.0

core 2.21.0
telemetry 1.0.6

Python location 'C:\Program Files (x86)\Microsoft SDKs\Azure\CLI2\python.exe'
Extensions directory 'C:\Users\shhender\.azure\cliextensions'

Python (Windows) 3.6.8 (tags/v3.6.8:3c6b436a57, Dec 23 2018, 23:31:17) [MSC v.1916 32 bit (Intel)]

---
#### Document Details

⚠ *Do not edit this section. It is required for docs.microsoft.com ➟ GitHub issue linking.*

* ID: 1e9c6366-3419-6303-85ab-1974cb741316
* Version Independent ID: bd0a7f67-c469-9684-18e4-9d67380bcec6
* Content: [az account management-group](https://docs.microsoft.com/en-us/cli/azure/account/management-group?view=azure-cli-latest)
* Content Source: [latest/docs-ref-autogen/account/management-group.yml](https://github.com/MicrosoftDocs/azure-docs-cli/blob/master/latest/docs-ref-autogen/account/management-group.yml)
* Service: **azure**
* GitHub Login: @rloutlaw
* Microsoft Alias: **routlaw**