Summary:
Generate t/run-* scripts to run tests in $PARALLEL_TEST separately, then make check_0 rule execute all of them.

Run `time make check` after running `make all`.
master: 71 sec
with this diff: 63 sec.

It seems moving more tests to $PARALLEL_TEST doesn't help improve test time though.

Test Plan:
Run the following
  make check
  J=16 make check
  J=1 make check
  make valgrind_check
  J=1 make valgrind_check
  J=16 make_valgrind_check

Reviewers: IslamAbdelRahman, sdong

Reviewed By: sdong

Subscribers: leveldb, kradhakrishnan, dhruba, andrewkr, yhchiang

Differential Revision: https://reviews.facebook.net/D56805