tty: move IO of master pty to be done with epoll

This moves all console code to use github.com/containerd/console library to
handle console I/O. Also move to use EpollConsole by default when user requests
a terminal so we can still cope when the other side temporarily goes away.

Signed-off-by: Daniel Dao <dqminh89@gmail.com>

vendor/github.com/containerd/console/console.go

@@ -0,0 +1,54 @@
+package console
+
+import (
+	"errors"
+	"io"
+	"os"
+)
+
+var ErrNotAConsole = errors.New("provided file is not a console")
+
+type Console interface {
+	io.Reader
+	io.Writer
+	io.Closer
+
+	// Resize resizes the console to the provided window size
+	Resize(WinSize) error
+	// ResizeFrom resizes the calling console to the size of the
+	// provided console
+	ResizeFrom(Console) error
+	// SetRaw sets the console in raw mode
+	SetRaw() error
+	// DisableEcho disables echo on the console
+	DisableEcho() error
+	// Reset restores the console to its orignal state
+	Reset() error
+	// Size returns the window size of the console
+	Size() (WinSize, error)
+	// Fd returns the console's file descriptor
+	Fd() uintptr
+}
+
+// WinSize specifies the window size of the console
+type WinSize struct {
+	// Height of the console
+	Height uint16
+	// Width of the console
+	Width uint16
+	x     uint16
+	y     uint16
+}
+
+// Current returns the current processes console
+func Current() Console {
+	return newMaster(os.Stdin)
+}
+
+// ConsoleFromFile returns a console using the provided file
+func ConsoleFromFile(f *os.File) (Console, error) {
+	if err := checkConsole(f); err != nil {
+		return nil, err
+	}
+	return newMaster(f), nil
+}