core: cleanup dumpvar

Summary:
Contains two small improvements:
  - Do not show TARGET_BUILD_APPS if TARGET_BUILD_APPS is unset
  - Correct erratic indentation

Test Plan: win

Reviewers: randall.rushing, Mustaavalkosta, Roach, synergy

Reviewed By: synergy

Differential Revision: http://review.codefirex.com/D330