Retry npm calls since they seem a bit unreliable.

utils.py

Index: utils.py
===================================================================
--- utils.py	(revision 293821)
+++ utils.py	(working copy)
@@ -11,9 +11,25 @@
 import sys
 import subprocess
 import tarfile
+import time
 import zipfile
 
 
+def RunSubprocessWithRetry(cmd):
+  """Invokes the subprocess and backs off exponentially on fail."""
+  for i in range(5):
+    try:
+      subprocess.check_call(cmd)
+      return
+    except subprocess.CalledProcessError as exception:
+      backoff = pow(2, i)
+      print 'Got %s, retrying in %d seconds...' % (exception, backoff)
+      time.sleep(backoff)
+  
+  print 'Giving up.'
+  raise exception
+
+
 def DownloadFilesFromGoogleStorage(path):
   print 'Downloading files in %s...' % path