Allow to download dependencies from insecure connections

SSL connections done by Curl will be attempted to be made secure by
using the CA certificated bundle but when the connection can be
established but not secured, Curl will not fail.

Change-Id: I9d2c61b4b3415c77bebb42db355b2a46424b91a7
diff --git a/tools/download_file.py b/tools/download_file.py
index 3e6fca9..ab8647d 100755
--- a/tools/download_file.py
+++ b/tools/download_file.py
@@ -110,7 +110,7 @@
 
   print('Download %s' % src_url, file=stderr)
   try:
-    check_call(['curl', '--proxy-anyauth', '-sfo', cache_ent, src_url])
+    check_call(['curl', '--proxy-anyauth', '-ksfo', cache_ent, src_url])
   except OSError as err:
     print('could not invoke curl: %s\nis curl installed?' % err, file=stderr)
     exit(1)