Summary:
One test in transaction_test.cc forgets to call SyncPoint::DisableProcessing().
As a result, a program might to access the SyncPoint singleton after it
already goes out of scope.
This patch fix this error by calling SyncPoint::DisableProcessing().
Test Plan: transaction_test
Reviewers: sdong, IslamAbdelRahman, kradhakrishnan, anthony
Reviewed By: anthony
Subscribers: dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D54033