<!--- Verify first that your issue is not already reported on GitHub -->
<!--- Also test if the latest release and devel branch are affected too -->
<!--- Complete *all* sections as described, this form is processed automatically -->

##### SUMMARY
<!--- Explain the problem briefly below -->
The snapshot module currently only supports storage blob as a creation source, it should
supports managed disk as a creation source. 
##### ISSUE TYPE
- Bug Report

##### COMPONENT NAME
<!--- Write the short name of the module, plugin, task or feature below, use your best guess if unsure -->
lib/ansible/modules/cloud/azure/azure_rm_snapshot.py
##### ANSIBLE VERSION
<!--- Paste verbatim output from "ansible --version" between quotes -->
```paste below
ansible 2.9.0
  config file = None
  configured module search path = [u'/home/haiyuan/.ansible/plugins/modules', u'/usr/share/ansible/plugins/modules']
  ansible python module location = /opt/ansible/local/lib/python2.7/site-packages/ansible
  executable location = /opt/ansible/bin/ansible
  python version = 2.7.12 (default, Oct  8 2019, 14:14:10) [GCC 5.4.0 20160609]
```
if isinstance(body, list):
            for item in body:
                self.inflate_parameters(spec, item, level)
            return
        for name in spec.keys():
            
            param = body.get(name)
            if not param:
                continue
            
            pattern = spec[name].get('pattern', None)
            if pattern:
                if pattern == 'camelize':
                    param = _snake_to_camel(param, True)
                else:
                    param = self.normalize_resource_id(param, pattern)
                    body[name] = param
            disposition = spec[name].get('disposition', '*')
            if level == 0 and not disposition.startswith('/'):
                continue
            if disposition == '/':
                disposition = '/*'
            parts = disposition.split('/')
            if parts[0] == '':
                
                parts.pop(0)
            target_dict = body
            elem = body.pop(name)
            while len(parts) > 1:
                target_dict = target_dict.setdefault(parts.pop(0), {})