Add basic logging to file support

This currently logs to a json file with the stream type.  This is slow
and hard on the cpu and memory so we need to swich this over to
something like protobufs for the binary logs but this is just a start.

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>

runtime/container.go

@@ -1,6 +1,7 @@
 package runtime
 
 import (
+	"io"
 	"os"
 	"time"
 
@@ -24,9 +25,24 @@ type State struct {
 	Status Status
 }
 
-type Stdio struct {
-	Stderr string
-	Stdout string
+type IO struct {
+	Stdin  io.WriteCloser
+	Stdout io.ReadCloser
+	Stderr io.ReadCloser
+}
+
+func (i *IO) Close() error {
+	var oerr error
+	for _, c := range []io.Closer{
+		i.Stdin,
+		i.Stdout,
+		i.Stderr,
+	} {
+		if err := c.Close(); oerr == nil {
+			oerr = err
+		}
+	}
+	return oerr
 }
 
 type Stat struct {