##### 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
ret = {}
    keyret = kms.get_key_policy(KeyId=keyarn, PolicyName='default')
    policy = json.loads(keyret['Policy'])
    changes_needed = {}
    
    had_invalid_entries = False
    for statement in policy['Statement']:
        for granttype in ['role', 'role grant', 'admin']:
            
            
            
            if not isinstance(statement.get('Principal'), dict):
                statement['Principal'] = dict()
            if 'AWS' in statement['Principal'] and isinstance(statement['Principal']['AWS'], string_types):
                
                statement['Principal']['AWS'] = [statement['Principal']['AWS']]
            if not isinstance(statement['Principal'].get('AWS'), list):
                statement['Principal']['AWS'] = list()
            if mode == 'grant' and statement['Sid'] == statement_label[granttype]:
                
                if granttype in granttypes:
                    invalid_entries = [item for item in statement['Principal']['AWS'] if not item.startswith('arn:aws:iam::')]
                    if clean_invalid_entries and invalid_entries:
                        
                        
                        valid_entries = [item for item in statement['Principal']['AWS'] if item.startswith('arn:aws:iam::')]
                        statement['Principal']['AWS'] = valid_entries
                        had_invalid_entries = True