Load etcd tarball from GCS.

Also fix up comment about how to cache docker debs.

(cherry picked from commit d033dfcc2b2f4b0cadfd27085245cbf72ba6ca29)
Install Salt from debs on GCS.

Also make downloading more reliable and run 'highstate' after install for good measure.  As part of this we no longer use gsutil to download and have to make 'staged' binaries in GCS publicly readable.

(cherry picked from commit 887c9b18d6e96bd3a1e476e9f1723a63d2df08cb)
Fix typo in README

(cherry picked from commit dba0f2d661d67f10c38cd7058a25945a59eaebe7)
Merge pull request #2271 from jbeda/release-0.4-gcs-deps

Cherrypick reliability tweaks for GCE deploy