Shutdown Heka if the sandbox decoder initialization fails
Don't repeat the last error message to avoid some confusion
Undo the refactoring that swallows the error

https://github.com/mozilla-services/heka/commit/3361dd99abfe886259095009d59f256bc79fac95#diff-2bb4eb5d697fe3a655462d1c684a0346L151
gofmt the file
Update error message per feedback
Add 'sandbox' to the error message
Merge pull request #895 from mozilla-services/decoder_init_check

Re-add the code to shutdown on a sandbox decoder initialization failure