Change http code from 200 to 500 when proxying error

Proxying request will throw exception but return 200 if the current
leader crashes, which may affect the judgement of user whether the job
is successful or not. Changing it to 500 to avoid this question.
Add http auth support to the PUT request
Update README.md

updating link & language
Update README.md
Merge pull request #320 from depay/master

Change http code from 200 to 500 when proxying error
Merge pull request #321 from flixster/p/stieg/http_auth_fix_script

Add http auth support to the PUT request