Add an advanced option to build_image so that a caller can specify the version.

This change adds the ability for a caller to pass a specific version name
to build_image rather than rely on parsing of chromeos_version.sh + attempt
number.

BUG=chromium-os:29077
TEST=Ran build_image w/ w/out option

Change-Id: I69b76ae4bfc148325686902606476a0aae293e56
Reviewed-on: https://gerrit.chromium.org/gerrit/21391
Reviewed-by: Brian Harring <ferringb@chromium.org>
Tested-by: Chris Sosa <sosa@chromium.org>
2 files changed