Fix ldb_test.py to hide garbage from std output

Fix ldb_test.py to hide garbage from std output

Summary: ldb_test.py did a lot of assertFalse checks and displayed all the failed messages on the std output making it confusing to tell a successful from a failed run. Also many empty lines used to be needlessly printed. Also added some progression-"feel-good" lines in the tests

Test Plan: python ldb_test.py

Reviewers: dhruba, sheki, dilipj, chip

Reviewed By: dilipj

CC: leveldb
Differential Revision: https://reviews.facebook.net/D9297