Merge pull request microsoft#1044 from katiewasnothere/fix_exec_in_sh…

…im_host

use requested stdio in call  to exec in shim host

internal/cmd/diag.go

@@ -9,7 +9,6 @@ import (
 	"github.com/Microsoft/hcsshim/internal/logfields"
 	"github.com/Microsoft/hcsshim/internal/shimdiag"
 	"github.com/Microsoft/hcsshim/internal/uvm"
-	errorspkg "github.com/pkg/errors"
 )
 
 // ExecInUvm is a helper function used to execute commands specified in `req` inside the given UVM.
@@ -48,13 +47,21 @@ func ExecInShimHost(ctx context.Context, req *shimdiag.ExecProcessRequest) (int,
 	if len(req.Args) > 1 {
 		cmdArgsWithoutName = req.Args[1:]
 	}
+	np, err := NewNpipeIO(ctx, req.Stdin, req.Stdout, req.Stderr, req.Terminal)
+	if err != nil {
+		return 0, err
+	}
+	defer np.Close(ctx)
 	cmd := exec.Command(req.Args[0], cmdArgsWithoutName...)
-	output, err := cmd.CombinedOutput()
+	cmd.Stdin = np.Stdin()
+	cmd.Stdout = np.Stdout()
+	cmd.Stderr = np.Stderr()
+	err = cmd.Run()
 	if err != nil {
 		if exiterr, ok := err.(*exec.ExitError); ok {
-			return exiterr.ExitCode(), errorspkg.Wrapf(exiterr, "command output: %v", string(output))
+			return exiterr.ExitCode(), exiterr
 		}
-		return -1, errorspkg.Wrapf(err, "command output: %v", string(output))
+		return -1, err
 	}
 	return 0, nil
 }