cv: shorten the tryjob refresh interval to 2.5 minutes
cv: shorten the tryjob refresh interval to 2.5 minutes

Reason: When I was testing yesterday, there seems to be a outage in
Pub/Sub and I have to wait for 10 minutes in order for CV to realize
Tryjob has ended. Lowering the interval to 2.5 minutes should keep
a good balance between latency and amount of call to Buildbucket

R=robertocn

Bug: 1312255
Change-Id: I994dba44ad29141c7efd59ce32c9f55c2072f352
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/3787399
Commit-Queue: Roberto Carrillo <b31161e510fbb37f8f70fdcde11530d2bae88470@chromium.org>
Auto-Submit: Yiwei Zhang <50b2a565e2e78c292794832469a30ce5abc9959c@google.com>
Reviewed-by: Roberto Carrillo <b31161e510fbb37f8f70fdcde11530d2bae88470@chromium.org>

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