Show better error messages for failed HTTP requests

[tiffon]

Description

Currently, failed HTTP requests trigger error messages that are ok in the case of 404s but are useless, otherwise.

Steps to reproduce the issue:

1. Try to view a trace that does not exist
2. Execute a search with the tag parameter as "a"
3. Run the UI (via checking out this repo) without a query-service running on the proxy port

Describe the results you received:

Step 1 yields a 404 HTTP response and the message "Resource not found in the Jaeger Query Service."

Step 2 yields a 400 HTTP response and the message "Bad JSON returned from the Jaeger Query Service."

Step 3 yields a 500 HTTP response and the message "Bad JSON returned from the Jaeger Query Service."

Describe the results you expected:

The 404 message is fine but should probably be handled in a more generic fashion.

The other responses take two forms: with JSON data describing the error and without JSON data.

Seems like all error messaging should work as follows:

• If there is JSON data, show the response status code and the message from the JSON data
• Otherwise, show the status code and the response text
• If there is no response text, show the status code and the message An unknown error was encountered

The only exception being the scenario described in #51, which will be addressed by that ticket.

Additional information you deem important (e.g. issue happens only occasionally):

Related issues:

• jaeger-query: "msg":"Failed to exec query","error":"Operation failed - received 0 responses and 1 failures" - wut? jaeger#418
• Can't find any spans... keep getting "Unexpected end of JSON input" jaeger#412
• UI gives confusing error messages jaeger#401