Putting a secret payload does not fail with an invalid mime-type

[Melissa Kam]

Steps to Reproduce:
POST http://.../v1/test_tenant/secrets
{
  "name": "AES key",
  "expiration": "2014-02-28T19:14:44.180394",
  "algorithm": "aes",
  "bit_length": 256,
  "cypher_type": "CBC",
  "payload_content_type": "text/plain; charset=utf-8"
}

PUT http://.../v1/test_tenant/secrets/{secret_ref}
{
gF6+lLoF3ohA9aPRpt+6bQ==
}
Headers:
Content-Type: invalid-type

Response:
200 OK