Make fetch shuffle partition data in parallel

[yahoNanJing]

Which issue does this PR close?

Closes #208.

Rationale for this change

What changes are included in this PR?

Are there any user-facing changes?

[yahoNanJing]

Hi @andygrove, @thinkharderdev, @avantgardnerio, could you help review this PR?

[mingmwang]

@yahoNanJing Could you please explain a little about the error handling case ? For example, if one of the parallel fetch failed, what happened to the others ? And what happened if there are multiple parallel fetch failures, will all the error info correctly propagated to the stream consumer ?

[yahoNanJing]

@mingmwang Just added one commit to abort fast when error occurs.