[Mgmt][Botservice] multi inheritance problem

- **Package Name**: azure-mgmt-boservice
- **Package Version**: 2.0.0b2
- **Operating System**: Linux/Windows
- **Python Version**: 3.7.0

**Describe the bug**
When initialize model `Site`, the following error will be raised:
```
> super(WebChatSite, self).__init__(**kwargs)
E TypeError: __init__() missing 2 required keyword-only arguments: 'site_name' and 'is_enabled'
```

**To Reproduce**
Steps to reproduce the behavior:
run the following code:
```
from azure.mgmt.botservice.models import Site

Site(
is_v1_enabled=True,
is_v3_enabled=True,
site_name="xxx",
is_enabled=True,
is_webchat_preview_enabled=True,
is_secure_site_enabled=True
)
```

**Expected behavior**
The model could be initialized successfully

**Screenshots**
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**Additional context**
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