##### 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
paginator = connection.get_paginator('list_aliases')
    return paginator.paginate().build_full_result()
def get_kms_aliases_lookup(connection):
    _aliases = dict()
    for alias in get_kms_aliases_with_backoff(connection)['Aliases']:
        
        if 'TargetKeyId' in alias:
            
            if alias['TargetKeyId'] in _aliases:
                _aliases[alias['TargetKeyId']].append(alias['AliasName'][6:])
            else:
                _aliases[alias['TargetKeyId']] = [alias['AliasName'][6:]]
    return _aliases
@AWSRetry.backoff(tries=5, delay=5, backoff=2.0)
def get_kms_tags_with_backoff(connection, key_id, **kwargs):
    return connection.list_resource_tags(KeyId=key_id, **kwargs)
@AWSRetry.backoff(tries=5, delay=5, backoff=2.0)
def get_kms_grants_with_backoff(connection, key_id):
    params = dict(KeyId=key_id)
    paginator = connection.get_paginator('list_grants')
    return paginator.paginate(**params).build_full_result()
@AWSRetry.backoff(tries=5, delay=5, backoff=2.0)
def get_kms_metadata_with_backoff(connection, key_id):
    return connection.describe_key(KeyId=key_id)
@AWSRetry.backoff(tries=5, delay=5, backoff=2.0)
def list_key_policies_with_backoff(connection, key_id):
    paginator = connection.get_paginator('list_key_policies')
    return paginator.paginate(KeyId=key_id).build_full_result()
@AWSRetry.backoff(tries=5, delay=5, backoff=2.0)
def get_key_policy_with_backoff(connection, key_id, policy_name):