pkg/archive: adjust chmod bits on windows

This change modifies the chmod bits of build context archives built on
windows to preserve the execute bit and remove the r/w bits from
grp/others.

Also adjusted integ-cli tests to verify permissions based on the platform
the tests are running.

Fixes #11047.

Signed-off-by: Ahmet Alp Balkan <ahmetalpbalkan@gmail.com>

archive/archive_windows.go

@@ -4,6 +4,7 @@ package archive
 
 import (
 	"fmt"
+	"os"
 	"strings"
 
 	"github.com/docker/docker/vendor/src/code.google.com/p/go/src/pkg/archive/tar"
@@ -23,6 +24,17 @@ func CanonicalTarNameForPath(p string) (string, error) {
 	return strings.Replace(p, "\\", "/", -1), nil
 }
 
+// chmodTarEntry is used to adjust the file permissions used in tar header based
+// on the platform the archival is done.
+func chmodTarEntry(perm os.FileMode) os.FileMode {
+	// Clear r/w on grp/others: no precise equivalen of group/others on NTFS.
+	perm &= 0711
+	// Add the x bit: make everything +x from windows
+	perm |= 0100
+
+	return perm
+}
+
 func setHeaderForSpecialDevice(hdr *tar.Header, ta *tarAppender, name string, stat interface{}) (nlink uint32, inode uint64, err error) {
 	// do nothing. no notion of Rdev, Inode, Nlink in stat on Windows
 	return