libdot: fetch: increase retry count

Currently we retry 4 times (so 5 attempts total).  Since we backoff by
x2 each time, that means our attempt window is <20 seconds before we
give up (1 + 2 + 4 + 8 = 15 seconds, plus network delays).  Increase
this to 7 retries (so 8 attempts total) which stretches us out to over
2 minutes in total.  If the server/network is having trouble, then this
is still reasonable.

Change-Id: I0a84a02a4414181534d76ca5c5de40b26df4e29f
Reviewed-on: https://chromium-review.googlesource.com/c/apps/libapps/+/7731981
Reviewed-by: Joel Hockey <joelhockey@chromium.org>
Tested-by: kokoro <noreply+kokoro@google.com>

libdot/bin/libdot.py

diff --git a/libdot/bin/libdot.py b/libdot/bin/libdot.py
index f12f40a..a45f347 100644
--- a/libdot/bin/libdot.py
+++ b/libdot/bin/libdot.py
@@ -561,7 +561,8 @@
     # This seems to be good enough for our needs.
     tmpfile = output if stream else output + ".tmp"
     backoff = 1
-    for attempt in range(0, 5):
+    MAX_ATTEMPTS = 8
+    for attempt in range(1, MAX_ATTEMPTS + 1):
         try:
             with open(tmpfile, "wb") as outfp:
                 fetch_data(
@@ -591,12 +592,14 @@
                     sys.exit(1)
 
             logging.warning("Download failed: %s", e)
-            if attempt < 4:
+            if attempt < MAX_ATTEMPTS:
                 logging.warning("Will retry after sleeping %s seconds", backoff)
                 time.sleep(backoff)
                 backoff *= 2
     else:
-        logging.error("Unabled to download; giving up")
+        logging.error(
+            "Unabled to download after %i attempts; giving up", MAX_ATTEMPTS
+        )
         if not stream:
             unlink(tmpfile)
         sys.exit(1)