api: improve log message of logging in with a user of another organization than the blockchain node

[Stezido]

If someone logs in with a user of another organization than the blockchain node is from the api throws following error:

api_1 | [2019-03-22 14:11:13.090 +0000] FATAL (TruBudget on f5fb80oc5958):
api_1 | msg: "BUG: Caught a non-Error type"
api_1 | error: {
api_1 | "kind": "decryption failed",
api_1 | "hexEncodedCiphertext": "03484c82feae3394a8cb585da8d11c643e026dbd64254b5f3cda47946e8ba7b9ea4981b94ca227880bac61de937dde94d60f403cccc57c0a3acbe55800780a8bc80ee917b20c0494c7833506d6a6bb22fcff0fe34684ad13e5bdd42fa"
api_1 | }
api_1 | Trace
api_1 | at convertError (/home/node/dist/http_errors.js:37:17)
api_1 | at Array.map ()
api_1 | at Object.toHttpError (/home/node/dist/http_errors.js:9:31)
api_1 | at Object.server.post (/home/node/dist/user_authenticate.js:152:50)

We should catch this error and give specific information what happened. Otherwise it leads to misunderstanding.