bb: increase (re)tries from 5 to 10, and bound max delay by 5min.
bb: increase (re)tries from 5 to 10, and bound max delay by 5min.

This shouldn't make a difference for most *working* uses cases of `bb`.
But this will make a difference for ChromeOS which uses dedicated
non-autoscaling "beefy" module (now, called "service") of Buildbucket
server, which in case of load-sheds requests after just 10s of inability
to serve them. In such cases,
  previously, total time between first and last try is just 50s.
  with this CL, it'll be >10 minutes.

R=vadimsh

Bug: 1030156
Change-Id: I1ece591ea071efb0eeea0407cf8ff4137d72b547
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/1947382
Reviewed-by: Vadim Shtayura <9f116ddb1b24f6fc1916a676eb17161b6c07dfc1@chromium.org>
Commit-Queue: Andrii Shyshkalov <a30c74fa30536fe7ea81ed6dec202e35e149e1fd@google.com>

luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go