cmd/upspinfs: fix test
cmd/upspinfs: fix test

We were incorrectly extracting the user name from a path.

Change-Id: Ib50d5ed677d9a28b19c25b92ac952f89f271191f
Reviewed-on: https://upspin-review.googlesource.com/6172
Reviewed-by: Eduardo Pinheiro <55040cbb39ba395339ae7940d8da6cd97797a4a8@google.com>

upspin/upspin,upspin/upspin