retry unix.EINTR for container init process

When running a script from an azure file share interrupted syscall
occurs quite frequently, to remedy this add retries around execve
syscall, when EINTR is returned.

Signed-off-by: Maksim An <maksiman@microsoft.com>

libcontainer/standard_init_linux.go

@@ -227,7 +227,7 @@ func (l *linuxStandardInit) Init() error {
 		return err
 	}
 
-	if err := unix.Exec(name, l.config.Args[0:], os.Environ()); err != nil {
+	if err := system.Exec(name, l.config.Args[0:], os.Environ()); err != nil {
 		return fmt.Errorf("can't exec user process: %w", err)
 	}
 	return nil