Print to stdout when spending a long time downloading files
Print to stdout when spending a long time downloading files

This must go to the stdout so that swarm or buildbot won't kill the test
if it takes more than 10 minutes to download all the required files,
which could occur if the machine has no cache.

TBR=vadimsh@chromium.org
BUG=

Review URL: https://chromiumcodereview.appspot.com/18645002

git-svn-id: d5a9b8648c52d490875de6588c8ee7ca688f9ed1@210001 0039d316-1c4b-4281-b951-d872f2087c98

luci/luci-py,luci/luci-py,luci/luci-py,luci/luci-py