[config] Reduce processing rate from 5/s to 4/s.
[config] Reduce processing rate from 5/s to 4/s.

We are still getting HTTP 429 from Gitiles, though only one or two per refresh
cycle (compared to like 100). Reduce the processing rate slightly more in
attempt to get rid of them.

4/s is still 8x larger than the theoretical minimal rate needed to process 300
config sets each 10 min.

R=ef4933a197ef7b4b3f55f1bec4942aead3637a2a@chromium.org

Change-Id: Ib81751f69dcc32980df1e9774695a871d8bd72c5
Reviewed-on: https://chromium-review.googlesource.com/c/1428999
Reviewed-by: Nodir Turakulov <ef4933a197ef7b4b3f55f1bec4942aead3637a2a@chromium.org>
Commit-Queue: Vadim Shtayura <9f116ddb1b24f6fc1916a676eb17161b6c07dfc1@chromium.org>

luci/luci-py,luci/luci-py,luci/luci-py,luci/luci-py