[cv][aggrmetrics] tune error condition.
[cv][aggrmetrics] tune error condition.

The following error has been happening about every two weeks,
and it's not actionable so tune it down a bit:
  aggrmetrics weren't flushed for a long time 2m7.505490413s

Now, the log will still contain warnings, but errors only if
this happens for >4 minutes, which is probably worth investigating
(e.g. we may have extreme CPU contention).

R=ddoman

Change-Id: Iadbc1169f812e61f2bb0b964d516fa44b5f14b02
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/3132926
Auto-Submit: Andrii Shyshkalov <a30c74fa30536fe7ea81ed6dec202e35e149e1fd@google.com>
Commit-Queue: Scott Lee <1dcb292530f82960316cb3d87cd67c3f212b79cb@chromium.org>
Reviewed-by: Scott Lee <1dcb292530f82960316cb3d87cd67c3f212b79cb@chromium.org>

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