Summary:
Added tests for two LDBCommands namely i) ManifestDumpCommand and ii) ListColumnFamiliesCommand.
+ Minor fix in the sscanf formatter (along relace C cast with C++ cast) + replacing localtime with localtime_r which is thread safe.

Test Plan: make all && ./tools/ldb_test.py

Reviewers: anthony, igor, IslamAbdelRahman, kradhakrishnan, lgalanis, rven, sdong

Reviewed By: sdong

Subscribers: leveldb, dhruba

Differential Revision: https://reviews.facebook.net/D45819