tools: fix AttributeError: __exit__ on Python 2.6

Error occurs while dealing with Tar archives

PR-URL: https://github.com/nodejs/node/pull/17663
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Steven R Loomis <srloomis@us.ibm.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

tools/configure.d/nodedownload.py

@@ -60,7 +60,7 @@ def unpack(packedfile, parent_path):
             icuzip.extractall(parent_path)
             return parent_path
     elif tarfile.is_tarfile(packedfile):
-        with tarfile.TarFile.open(packedfile, 'r') as icuzip:
+        with contextlib.closing(tarfile.TarFile.open(packedfile, 'r')) as icuzip:
             print ' Extracting tarfile: %s' % packedfile
             icuzip.extractall(parent_path)
             return parent_path