[spantest] Further sanitize db name
[spantest] Further sanitize db name

1) Guarantee lower case
2) Guarantee len <= 30

Now tests pass on CQ: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/1852965/7

R=jchinlee@chromium.org, 9f116ddb1b24f6fc1916a676eb17161b6c07dfc1@chromium.org

Change-Id: Iaa9ea69ff83d3eb0e80bfea8c0d56187a64e8ae4
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/1869294
Auto-Submit: Nodir Turakulov <ef4933a197ef7b4b3f55f1bec4942aead3637a2a@chromium.org>
Commit-Queue: Vadim Shtayura <9f116ddb1b24f6fc1916a676eb17161b6c07dfc1@chromium.org>
Reviewed-by: Vadim Shtayura <9f116ddb1b24f6fc1916a676eb17161b6c07dfc1@chromium.org>

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