TBR: Ignore errors from "make distclean" in snappy.

If snappy has never been built before, the Makefile does not exist, and
running "make distclean" errors with:
    make: *** No rule to make target `distclean'. Stop.

We correctly ignore this error, but it ends up getting printed to the
console, which can be confusing.  This CL discards the output from "make
distclean".

Fixes https://github.com/vanadium/issues/issues/1227

Change-Id: I167480ff187c64c9f3eb9578e739fb51c9c14111
diff --git a/jiri-profile-v23/syncbase_profile/syncbase.go b/jiri-profile-v23/syncbase_profile/syncbase.go
index f008463..921a673 100644
--- a/jiri-profile-v23/syncbase_profile/syncbase.go
+++ b/jiri-profile-v23/syncbase_profile/syncbase.go
@@ -9,6 +9,7 @@
 	"bytes"
 	"flag"
 	"fmt"
+	"io/ioutil"
 	"os"
 	"path/filepath"
 	"runtime"
@@ -359,8 +360,8 @@
 	installSnappyFn := func() error {
 		s := jirix.NewSeq()
 		snappySrcDir := m.snappySrcDir.Abs(jirix)
-		// ignore errors from make distclean.
-		s.Pushd(snappySrcDir).Last("make", "distclean")
+		// Ignore errors from make distclean.
+		s.Pushd(snappySrcDir).Capture(ioutil.Discard, ioutil.Discard).Last("make", "distclean")
 		if err := s.Pushd(snappySrcDir).
 			Last("autoreconf", "--install", "--force", "--verbose"); err != nil {
 			return err