This should fix the problem where we see the first test
taking negative time, as well as possibly other issues
with performance tests which may be sensitive to changes
in wall clock time.

Fixes #398

This should more reliably shut down pexpect subprocesses when
build.py exits before completion.

file no longer returns image size on 14.04
fixes #373

Fixes #372

This is added because we install Ubuntu from a serial console.
Fixes #265

should facilitate importing 64-bit image

fixes #261