This CL adds a new script that automates building and uploading new
sysroot images.  Previously, you had to run UpdatePackageListsAll,
BuildSysrootAll, and UploadSysrootAll for each of the 4
sysroot-creators.  Then, you had to manually update the revision and
sha1sum in install_sysroot.py.  Now, simply run build_and_upload.py
and your CL should be ready to go.  In addition, the script
concurrently updates each sysroot image (there are currently 11 of
them), greatly reducing the time it took to update the sysroots.

In addition to adding the script, this CL also rolls all sysroots.

R=dpranke@chromium.org

Review-Url: https://codereview.chromium.org/2567123002
Cr-Commit-Position: refs/heads/master@{#438862}