Fix deadlock in HdfsScanNode.
Fix deadlock in HdfsScanNode.

Change-Id: I74a38f30c7793c4ace9d2446850a42e821f68bf2
Reviewed-on: http://gerrit.ent.cloudera.com:8080/2582
Reviewed-by: Henry Robinson <3eca10f30041813f045165784e24b5a950a6cc7e@cloudera.com>
Tested-by: jenkins

placrosse/ImpalaToGo,gistic/PublicSpatialImpala,gistic/PublicSpatialImpala,AtScaleInc/Impala,gistic/PublicSpatialImpala,placrosse/ImpalaToGo,ImpalaToGo/ImpalaToGo,rampage644/impala-cut,ImpalaToGo/ImpalaToGo,ImpalaToGo/ImpalaToGo,ImpalaToGo/ImpalaToGo,andybab/Impala,andybab/Impala,andybab/Impala,ImpalaToGo/ImpalaToGo,gistic/PublicSpatialImpala,andybab/Impala,placrosse/ImpalaToGo,AtScaleInc/Impala,placrosse/ImpalaToGo,gistic/PublicSpatialImpala,AtScaleInc/Impala,andybab/Impala,andybab/Impala,rampage644/impala-cut,AtScaleInc/Impala,AtScaleInc/Impala,AtScaleInc/Impala,gistic/PublicSpatialImpala,placrosse/ImpalaToGo,ImpalaToGo/ImpalaToGo,rampage644/impala-cut,rampage644/impala-cut,placrosse/ImpalaToGo,rampage644/impala-cut,rampage644/impala-cut