tools/presubmit: use "git reset --hard origin/master" to reset a local branch.
tools/presubmit: use "git reset --hard origin/master" to reset a local branch.

"git reset --hard HEAD" only resets to the last committed state. If for some
reaons we have several commits ahead in the master branch this won't work.

Change-Id: Idfcacb5c5e16735e5da47c57c6c530fa44d06547

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