Summary:
Add option '--show_properties' to sst_dump tool to allow displaying
property block of the specified files.

Test Plan:
Run sst_dump with the following arguments, which covers cases affected by
this diff:

  1. with only --file
  2. with both --file and --show_properties
  3. with --file, --show_properties, and --from

Reviewers: kailiu, xjin

Differential Revision: https://reviews.facebook.net/D15453