luci-py/isolateserver.py: Add archive support when downloading.

client/cipd.py

Index: client/cipd.py
diff --git a/client/cipd.py b/client/cipd.py
index 6065dbf81f13c2f3d8fb70ea4578bfea71c7c528..1f7d6b96fefa75bb2f33814cc7aa6d39447a90bc 100644
--- a/client/cipd.py
+++ b/client/cipd.py
@@ -356,7 +356,8 @@ def get_client(
       # cache by hashing it.
       version_digest = hashlib.sha1(version).hexdigest()
       try:
-        instance_id = version_cache.read(version_digest)
+        with version_cache.getfileobj(version_digest) as f:
+          instance_id = f.read()
       except isolateserver.CacheMiss:
         instance_id = resolve_version(
             service_url, package_name, version, timeout=timeoutfn())
@@ -381,8 +382,10 @@ def get_client(
     binary_path = unicode(os.path.join(cache_dir, 'cipd' + EXECUTABLE_SUFFIX))
     if fs.isfile(binary_path):
       file_path.remove(binary_path)
-    instance_cache.hardlink(instance_id, binary_path, 0511)  # -r-x--x--x
-
+    isolateserver.putfile(
+        instance_cache.getfileobj(instance_id),

[nodir, 2016/06/21 22:20:05]

here too

[mithro, 2016/06/22 12:03:10]

Done.

+        binary_path,
+        0511)  # -r-x--x--x
     yield CipdClient(binary_path)