Merge pull request #197 from aarondav/patrick-fix

Fix 'timeWriting' stat for shuffle files

Due to concurrent git branches, changes from shuffle file consolidation patch
caused the shuffle write timing patch to no longer actually measure the time,
since it requires time be measured after the stream has been closed.

(cherry picked from commit 972171b9d93b07e8511a2da3a33f897ba033484b)
Signed-off-by: Reynold Xin <rxin@apache.org>