devtools/presubmit: update Google storage prefix for presubmit results.
devtools/presubmit: update Google storage prefix for presubmit results.

Will update dashboard code in a separate CL.

Change-Id: I6531fee9266c32142ea928ea798dd970ffd8629c

vanadium/go.devtools,vanadium/go.devtools,vanadium/go.devtools