Summary:
Valgrind does not work well with JEMALLOC. If you run
a simple make valgrind_check, you will see lots of issues and
crashes. When precommit runs, this is taken care of. Here we
make sure valgrind_check is passed in DISABLE_JEMALLOC=1

Test Plan: Ran local valgrind_test and noticed the difference

Reviewers: IslamAbdelRahman

Reviewed By: IslamAbdelRahman

Subscribers: andrewkr, dhruba

Differential Revision: https://reviews.facebook.net/D65379