Adds the concept of invalid bucket.

Whenever a pull fails, we cannot compute a correct metric for this
bucket. Whether the failures happen at the beginning, in the middle or
at the end of the bucket, we cannot trust the data inside the bucket.

Let's say we have a metric with a screen on condition, a bucket size of
4 hours and we have the following events:
- h+0 bucket start -- screen is on -- data pull failed
- h+2 screen off -- pull succeed
- h+3 screen on -- pull succeed
- h+4 bucket end -- screen on -- pull succeed

The current logic will be wrong, it will ignore any data between h+0
and h+2. That timespan might be a huge contributor of the total bucket
value so this is wrong to keep any data from this bucket.

We also extend the concept of invalid buckets to other problems like a
pull being too long.

Bug: 123866830
Test: atest statsd_test
Change-Id: I300ab05cd7582cd2d7af9167de8d99b349071f0d