cmd/admin: permit deploy from non-Linux machines
cmd/admin: permit deploy from non-Linux machines

Also mv the binary from /tmp instead of cp'ing it,
to avoid leaving dregs behind.

Change-Id: Id5c417854551671f322c3da1b67c4a287947f66d
Reviewed-on: https://upspin-review.git.corp.google.com/1992
Reviewed-by: Eduardo Pinheiro <55040cbb39ba395339ae7940d8da6cd97797a4a8@google.com>

upspin/upspin,upspin/upspin