We have an alert on `not_enough_shares_for_audit` which fires too
frequently. Every time so far, it has been because of a network blip of
some nature on the satellite side.
Satellite operators are expected to have other means in place for
alerting on network problems and fixing them, so it's not necessary for
the audit framework to act in that way.
Instead, in this change, we add three new metrics,
`audit_not_enough_nodes_online`, `audit_not_enough_shares_acquired`, and
`audit_suspected_network_problem`. When an audit fails, and emits
`not_enough_shares_for_audit`, we will now determine whether it looks
like we are having network problems (most errors are connection
failures, possibly also some successful connections which subsequently
time out) or whether something else has happened.
After this is deployed, we can remove the alert on
`not_enough_shares_for_audit` and add new alerts on
`audit_not_enough_nodes_online` and `audit_not_enough_shares_acquired`.
`audit_suspected_network_problem` does not need an alert.
Refs: https://github.com/storj/storj/issues/4669
Change-Id: Ibb256bc19d2578904f71f5229111ac98e5212fcb
802ff18bd8