Summary:
Moved all the tests that verify property correctness into a separate
file. The goal is to reduce compile time and complexity of db_test. I didn't
add parallelism for db_properties_test, even though these tests were
parallelized in db_test, since the file is small enough that it won't matter.

Some of these moves may be controversial since it's hard to say whether the
test is "verifying property correctness," or "using properties to verify
rocksdb's correctness." I'm interested in any opinions.

Test Plan: ran db_properties_test, also waiting on "make commit-prereq -j32"

Reviewers: yhchiang, IslamAbdelRahman, sdong

Reviewed By: sdong

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D52995