misc/ios: increase iOS test harness timeout

The "lldb start" phase often times out on the iOS builder. Increase
the timeout and see if that helps.

Change-Id: I92fd67cbfa90659600e713198d6b2c5c78dde20f
Reviewed-on: https://go-review.googlesource.com/41863Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Elias Naur <elias.naur@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

misc/ios/go_darwin_arm_exec.go

@@ -346,7 +346,7 @@ func newSession(appdir string, args []string, opts options) (*lldbSession, error
 		i2 := s.out.LastIndex([]byte(" connect"))
 		return i0 > 0 && i1 > 0 && i2 > 0
 	}
-	if err := s.wait("lldb start", cond, 10*time.Second); err != nil {
+	if err := s.wait("lldb start", cond, 15*time.Second); err != nil {
 		panic(waitPanic{err})
 	}
 	return s, nil