Use nfs3 on rpis
Use nfs3 on rpis

Without this, it defaults to using nfs2 and UDP.  NFS3 uses TCP by default
and has some other improvments.  I think NFSv3 will be easier to load balance.

BUG=skia:

Review-Url: https://codereview.chromium.org/1965043003

google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot