##### SUMMARY

If you attempt to modify the policy on an existing KMS CMK using aws_kms's "policy" option this doesn't appear to get updated.

##### ISSUE TYPE
- Bug Report

##### COMPONENT NAME
lib/ansible/modules/cloud/amazon/aws_kms.py

##### ANSIBLE VERSION

```
ansible 2.8.1
  config file = /home/mchappel/.ansible.cfg
  configured module search path = [u'/home/mchappel/.ansible/plugins/modules', u'/usr/share/ansible/plugins/modules']
  ansible python module location = /usr/lib/python2.7/site-packages/ansible
  executable location = /usr/bin/ansible
  python version = 2.7.5 (default, Jun 11 2019, 12:19:05) [GCC 4.8.5 20150623 (Red Hat 4.8.5-36)]
```

##### CONFIGURATION

```
DEFAULT_CALLBACK_WHITELIST(/home/mchappel/.ansible.cfg) = [u'timer', u'profile_tasks']
HOST_KEY_CHECKING(/home/mchappel/.ansible.cfg) = False
RETRY_FILES_ENABLED(/home/mchappel/.ansible.cfg) = False
```

##### OS / ENVIRONMENT
RHEL7 + AWS


##### STEPS TO REPRODUCE

- Create KMS CMK
- Attempt to update policy using the 'policy' option on aws_kms

```
    - name: 'Update policy on KMS Keys'
      aws_kms:
        key_id: '{{ kms_key.id }}'
        alias: '{{ kms_key.alias | default(omit) }}'
        policy: ' {{ kms_current_policy | to_json }}'
```

##### EXPECTED RESULTS
KMS Policy is updated

##### ACTUAL RESULTS
KMS Policy stays the same
'''Since the policy seems a little, uh, fragile, make sure we know approximately what we're looking at.'''
    errors = []
    if policy['Version'] != "2012-10-17":
        errors.append('Unknown version/date ({0}) of policy. Things are probably different than we assumed they were.'.format(policy['Version']))
    found_statement_type = {}
    for statement in policy['Statement']:
        for label, sidlabel in statement_label.items():
            if statement['Sid'] == sidlabel:
                found_statement_type[label] = True
    for statementtype in statement_label.keys():
        if not found_statement_type.get(statementtype):
            errors.append('Policy is missing {0}.'.format(statementtype))
    if len(errors):
        raise Exception('Problems asserting policy shape. Cowardly refusing to modify it: {0}'.format(' '.join(errors)) + "\n" + str(policy))
    return None
def main():