net/nettest: deflake TestPipeTimeout

The block-write and block-read tests are both flaky,
because each assumes it can get a normal read/write
completed within 10ms. This isn’t always true.

We can’t increase the timeouts, because that slows down the test.
However, we don’t need to issue a regular read/write for this test.
The immediately preceding tests already test this code,
using a far more generous timeout.

Remove the extraneous read/write.

This drops the failure rate from 1 per 20,000 to undetectable
on my machine.

While we’re here, fix a typo in a debug print statement.

Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>

net/nettest/pipe.go

@@ -76,7 +76,7 @@ func (p *Pipe) Read(b []byte) (n int, err error) {
 	if debugPipe {
 		orig := b
 		defer func() {
-			log.Printf("Pipe(%q).Read( %q) n=%d, err=%v", p.name, string(orig[:n]), n, err)
+			log.Printf("Pipe(%q).Read(%q) n=%d, err=%v", p.name, string(orig[:n]), n, err)
 		}()
 	}
 	for n == 0 {