all: pass log IDs as the proper type rather than strings

This change focuses on the backend log ID, which is the mostly commonly
used in the client.  Tests which don't seem to make use of the log ID
just use the zero value.

Signed-off-by: Will Norris <will@tailscale.com>

ssh/tailssh/tailssh_test.go

@@ -38,6 +38,7 @@ import (
 	"tailscale.com/tempfork/gliderlabs/ssh"
 	"tailscale.com/tstest"
 	"tailscale.com/types/logger"
+	"tailscale.com/types/logid"
 	"tailscale.com/types/netmap"
 	"tailscale.com/util/cibuild"
 	"tailscale.com/util/lineread"
@@ -505,7 +506,7 @@ func TestSSH(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
-	lb, err := ipnlocal.NewLocalBackend(logf, "",
+	lb, err := ipnlocal.NewLocalBackend(logf, logid.PublicID{},
 		new(mem.Store),
 		new(tsdial.Dialer),
 		eng, 0)