##### 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 = kms.list_aliases()
    key_id = None
    for a in ret['Aliases']:
        if a['AliasName'] == aliasname:
            key_id = a['TargetKeyId']
            break
    if not key_id:
        raise Exception('could not find alias {0}'.format(aliasname))
    
    
    ret = kms.list_keys()
    for k in ret['Keys']:
        if k['KeyId'] == key_id:
            return k['KeyArn']
    raise Exception('could not find key from id: {0}'.format(key_id))
def get_arn_from_role_name(iam, rolename):
    ret = iam.get_role(RoleName=rolename)
    if ret.get('Role') and ret['Role'].get('Arn'):
        return ret['Role']['Arn']
    raise Exception('could not find arn for name {0}.'.format(rolename))
def do_policy_grant(kms, keyarn, role_arn, granttypes, mode='grant', dry_run=True, clean_invalid_entries=True):