Add firmware tarball to the list of build artifacts to download

Firmware build artifacts need to be available for reprogramming DUTs
in the autotest lab. This change includes the entire firmware tarball
(~16MB in size) into the set of files downloaded from gs image
archive. Missing firmware tarball will not cause a failure.

BUG=chromium-os:37467
TEST=manual
  . start a local instance of devserver
     ./devserver.py --archive_dir=/var/devserver --logfile=/tmp/devserver.log
  . in a different terminal ran
    $ for cmd in download wait_for_status
      do
        curl http://localhost:8080/$cmd?archive_url='gs://chromeos-image-archive/link-release/R26-3494.0.0'
      done
    $ ls -ltr /var/devserver/link-release/R26-3494.0.0/
    total 444592
    -rw-r--r-- 1 vbendeb vbendeb         0 Jan  1 16:57 cros-dell0.CP%20Server%20Thread-6-30156
    -rw-r--r-- 1 vbendeb vbendeb         0 Jan  1 16:57 chromiumos_test_image.bin
    drwxr-xr-x 4 vbendeb vbendeb      4096 Jan  1 16:57 au/
    -rw-r--r-- 1 vbendeb vbendeb 372863714 Jan  1 16:57 update.gz
    -rw-r--r-- 1 vbendeb vbendeb  66435120 Jan  1 16:57 stateful.tgz
    -rw-r--r-- 1 vbendeb vbendeb  15928789 Jan  1 16:57 firmware_from_source.tar.bz2
    drwxr-xr-x 7 vbendeb vbendeb     24576 Jan  1 16:58 autotest/
    -rw-r--r-- 1 vbendeb vbendeb         0 Jan  1 16:58 staged.timestamp

Change-Id: I6d19abe046eae5f0ef8739230a758fd5934919a6
Reviewed-on: https://gerrit.chromium.org/gerrit/40258
Tested-by: Vadim Bendebury <vbendeb@chromium.org>
Reviewed-by: Chris Sosa <sosa@chromium.org>
Commit-Queue: Vadim Bendebury <vbendeb@chromium.org>
diff --git a/build_artifact.py b/build_artifact.py
index 51dc698..3690390 100644
--- a/build_artifact.py
+++ b/build_artifact.py
@@ -14,14 +14,15 @@
 
 
 # Names of artifacts we care about.
-DEBUG_SYMBOLS = 'debug.tgz'
-STATEFUL_UPDATE = 'stateful.tgz'
-TEST_IMAGE = 'chromiumos_test_image.bin'
-ROOT_UPDATE = 'update.gz'
 AUTOTEST_PACKAGE = 'autotest.tar'
 AUTOTEST_ZIPPED_PACKAGE = 'autotest.tar.bz2'
-TEST_SUITES_PACKAGE = 'test_suites.tar.bz2'
+DEBUG_SYMBOLS = 'debug.tgz'
+FIRMWARE_ARCHIVE = 'firmware_from_source.tar.bz2'
 IMAGE_ARCHIVE = 'image.zip'
+ROOT_UPDATE = 'update.gz'
+STATEFUL_UPDATE = 'stateful.tgz'
+TEST_IMAGE = 'chromiumos_test_image.bin'
+TEST_SUITES_PACKAGE = 'test_suites.tar.bz2'
 
 
 class ArtifactDownloadError(Exception):