installer: force updating firmware in factory install mode.

installer: force updating firmware in factory install mode.

Factory test images (and install shims) are configured with
"leave_firmware_alone" because they may contain firmware blobs that are
different from the real version to install.

So we have to explicitly assign the "force" flag when factory installer is
trying to update the firmware to the assigned version (by make_factory_package
--firmwareupdate).

NOTE: This CL is to install firmware from the release images;
factory process using make_factory_packages is managed by http://codereview.chromium.org/6806001/

BUG=chrome-os-partner:3152
TEST=tagged .force_update_firmware and see updating messages

Change-Id: I449de11cb1785fd69890527313fbdce18f8b835f

R=wfrichar@chromium.org,rspangler@chromium.org

Committed: http://chrome-svn/viewvc/chromeos?view=rev&revision=4ae18e7

[Randall Spangler, 2011-04-05 16:29:03]

LGTM