Windows Secure Container Executor: the privileged file operations of hadoopwinutilsvc should be constrained to localdirs only

YARN-2458 added file manipulation operations executed in an elevated context by hadoopwinutilsvc. W/o any constraint, the NM (or a hijacker that takes over the NM) can manipulate arbitrary OS files under highest possible privileges, an easy elevation attack vector. The service should only allow operations on files/directories that are under the configured NM localdirs. It should read this value from wsce-site.xml, as the yarn-site.xml cannot be trusted, being writable by Hadoop admins (YARN-2551 ensures wsce-site.xml is only writable by system Administrators, not Hadoop admins).