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##### 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]
```
else:
                    new = sorted(new)
                    old = sorted(old)
                for i in range(len(new)):
                    if not self.default_compare(modifiers, new[i], old[i], path + '/*', result):
                        comparison_result = False
            return comparison_result
        else:
            updatable = modifiers.get(path, {}).get('updatable', True)
            comparison = modifiers.get(path, {}).get('comparison', 'default')
            if comparison == 'ignore':
                return True
            elif comparison == 'default' or comparison == 'sensitive':
                if isinstance(old, string_types) and isinstance(new, string_types):
                    new = new.lower()
                    old = old.lower()
            elif comparison == 'location':
                if isinstance(old, string_types) and isinstance(new, string_types):
                    new = new.replace(' ', '').lower()
                    old = old.replace(' ', '').lower()
            if str(new) != str(old):
                result['compare'].append('changed [' + path + '] ' + str(new) + ' != ' + str(old) + ' - ' + str(comparison))
                if updatable:
                    return False
                else:
                    self.module.warn("property '" + path + "' cannot be updated (" + str(old) + "->" + str(new) + ")")
                    return True
            else:
                return True