Elasticsearch policy sending DomainName as Dict, expect STR

[theotherothermatt]

Describe the bug
Lambdas created using the Elasticsearch policy are passing the DomainName to the AWS API as a dictionary, and the API needs it to be a string. You can find a gist of the full error here: https://gist.github.com/theotherothermatt/199f78ee33c0044dd2365583c9c3f604

Rolled back to version 0.9.1 and problem does not exist. There were commits to elasticsearch.py in both 0.9.2 and 0.9.3, so I think that the problem resides somewhere in those bug fixes.

To Reproduce
With c7n==0.9.3, use policy:

    mode:
        type: cloudtrail
        role: arn:aws:iam::<$account-id>:role/the-correct-role
        events:
         - source: es.amazonaws.com
           event: CreateElasticsearchDomain
           ids: "requestParameters.domainName"
    filters:
      - type: value
        key: "EncryptionAtRestOptions.Enabled"
        value: false
    actions:
        - type: delete

Then create an ES domain that is not encrypted at rest. Error will be in log stream.

Roll back to c7n==0.9.1
Try the above policy again (on a new lambda of course)
Domain will be deleted with no error

Expected behavior
The ES Domain will be deleted

Background (please complete the following information):

• OS: OSx 10.15.5
• Python Version: python 3.7.7
• Custodian Version: 0.9.3
• Cloud Provider: AWS
• Policy: [please exclude any account/sensitive information]

    mode:
        type: cloudtrail
        role: arn:aws:iam::<$account-id>:role/the-correct-role
        events:
         - source: es.amazonaws.com
           event: CreateElasticsearchDomain
           ids: "requestParameters.domainName"
    filters:
      - type: value
        key: "EncryptionAtRestOptions.Enabled"
        value: false
    actions:
        - type: delete

• custodian version --debug output
  Custodian: 0.9.3
  Python: 3.7.7 (default, Mar 10 2020, 15:43:03)
  [Clang 11.0.0 (clang-1100.0.33.17)]
  Platform: posix.uname_result(sysname='Darwin', nodename='', release='19.5.0', version='Darwin Kernel Version 19.5.0: Tue May 26 20:41:44 PDT 2020; root:xnu-6153.121.2~2/RELEASE_X86_64', machine='x86_64')
  Using venv: False
  Docker: False
  Installed:

argcomplete==1.11.1
attrs==19.3.0
boto3==1.13.24
botocore==1.16.24
docutils==0.15.2
importlib-metadata==1.6.1
jmespath==0.10.0
jsonschema==3.2.0
pyrsistent==0.16.0
python-dateutil==2.8.1
pyyaml==5.3.1
s3transfer==0.3.3
setuptools==46.0.0
six==1.15.0
tabulate==0.8.7
urllib3==1.25.9
zipp==3.1.0

[kapilt]

I think this was fixed in #5796 (trunk only) but worth confirming

[kapilt]

confirmed issue exhibits on trunk, fix up in #5920