Provides proper error handling on builder unpickle

This patch provides the necessary error handling while unpickling
a builder file. Earlier if a builder file is empty/invalid/corrupted,
the stacktrace was shown to user with an exit code of 1. This fixes it
to show a user-friendly message and also returns the exit code of 2,
indicating there was a failure.

Change-Id: I51eb24702c422299629f8053d4591dd10f5863f8
Closes-Bug: #1370680
Merge "Provides proper error handling on builder unpickle"