Fully migrate gsutil module to gcloud storage

[ViniciustCosta]

Fully migrate the gsutil module to use gcloud storage by:

• Removing the feature flags used during the migration;
• Migrating the name for the gcloud storage runner;
• Fixing some inconsistencies in the gcloud storage runner to match the behavior used by gsutil (e.g., add --recursive to rsync, add quiet flag -q, etc);
• Adjusting the unit tests

Temporarily retained the gsutil.py filename to facilitate revision, as changing the filename would highlight all the code and not only the actual changes (to be done in a follow-up PR).

Temporarily retained the GSUTIL_PATH as a fallback, since changing this to GCLOUD_PATH would depend on landing changes on chrome fuzzing infra init scripts.

DO NOT MERGE yet, as we need to wait for updating the gcloud on the mac and android bots.