store/remote: do not make a network call during Dial
store/remote: do not make a network call during Dial

Now that the bind package assumes that Dials happen instantaneously we
must prevent the store/remote from probing for a HTTP fast path during
Dial. This change defers that probe until the first Get request.

Change-Id: I673a2d8ccba4774c27f49a1b54b0ebe10370831a
Reviewed-on: https://upspin-review.googlesource.com/11880
Reviewed-by: Rob Pike <4dc7c9ec434ed06502767136789763ec11d2c4b7@golang.org>

upspin/upspin,upspin/upspin