API changes in vault 0.10.0 causes test to fail.

Since Vault 0.10.0 the K/V engine is versioned by default and returns the following warning:

Invalid path for a versioned K/V secrets engine. See the API docs for the appropriate API endpoints to use. If using the Vault CLI, use 'vault kv put' for this operation.

The warning can be seen at:

$ curl \
    --header "X-Vault-Token: $VAULT_TOKEN" \
    --request POST \
    --data '{"value": "bar"}' \
    http://127.0.0.1:8200/v1/secret/foo

### Formatted JSON Data returned by curl
{
  "request_id":"48b76803-c396-8f71-0d98-b5949478de2c",
  "lease_id":"",
  "renewable":false,
  "lease_duration":0,
  "data":null,
  "wrap_info":null,
  "warnings":[
    "Invalid path for a versioned K/V secrets engine. See the API docs for the appropriate API endpoints to use. If using the Vault CLI, use 'vault kv put' for this operation."
  ],
  "auth":null
}

---

The VaultKeyManager._store_key_value method doesn't care for the "warnings" value and just returns the key_id, but the data was actually not stored.

The required fixes are in the url (add 'data/' after secret/) and the request data is now {"data":{...}} instead of just {...}.

$ curl \
    --header "X-Vault-Token: $VAULT_TOKEN" \
    --request POST \
    --data '{"data":{"value": "bar"}}' \
    http://127.0.0.1:8200/v1/secret/data/foo

### Formatted JSON Data returned by curl
{
  "request_id":"087e314a-c2aa-7261-f004-99f07783e14f",
  "lease_id":"",
  "renewable":false,
  "lease_duration":0,
  "data":{
    "created_time":"2018-08-22T09:58:47.245643874Z",
    "deletion_time":"",
    "destroyed":false,
    "version":1
  },
  "wrap_info":null,
  "warnings":null,
  "auth":null
}

The equivalent fixes are also required in VaultKeyManager.get().