[hadoop] remove duplicate diagnostics

[mzmssg]

More readable patch: https://github.com/mzmssg/hadoop/pull/4/files
There will no duplicate stderr in diagnostics:
Original

Fixed

[coveralls]

Coverage remained the same at 52.932% when pulling bf49219 on zimiao/remove_duplicate_diagnostics into 07e4e5f on master.

[coveralls]

Coverage remained the same at 52.932% when pulling bf49219 on zimiao/remove_duplicate_diagnostics into 07e4e5f on master.

[yqwang-ms]

Can we just move line 1575 to 1579 and 1596?
It seems more nature.

[mzmssg]

It's the same. But we need three if (exitEvent.getDiagnosticInfo() != null) in different block, and split diagnostic and its prefix Diagnostic message from attempt in different blocks.
I don't think it's more readable.

[yqwang-ms]

It should be different style, I perfer functional style, anyway it is fine.