Revoke a grant from a key.

    CLI example::

        salt myminion boto_kms.revoke_grant 'alias/mykey' 8u89hf-j09j...

def revoke_grant(key_id, grant_id, region=None, key=None, keyid=None,
                 profile=None):
    '''
    Revoke a grant from a key.

    CLI example::

        salt myminion boto_kms.revoke_grant 'alias/mykey' 8u89hf-j09j...
    '''
    conn = _get_conn(region=region, key=key, keyid=keyid, profile=profile)

    if key_id.startswith('alias/'):
        key_id = _get_key_id(key_id)
    r = {}
    try:
        conn.revoke_grant(key_id, grant_id)
        r['result'] = True
    except boto.exception.BotoServerError as e:
        r['result'] = False
        r['error'] = __utils__['boto.get_error'](e)
    return r