Report I/O errors in the stats of the service encountering the errors

[jfsmig]

Actions are necessary when a broken partition is encountered.

A lot of possibilities:

• raise an high-level alert destined to an operator
• automatically trigger a rebuild of the nearly-broken partition, to an other location
• automatically set to 0 the score of the service
• any combination of those possibilities

[jfsmig]

Currently managed for services based on sqliterepo, in #1395