This adds a singleton `timeout` package that will allow services and user
to configure timeouts in the daemon. When a service wants to use a
timeout, it should declare a const and register it's default value
inside an `init()` function for that package. When the default config
is generated, we can use the `timeout` package to provide the available
timeout keys so that a user knows that they can configure.
These show up in the config as follows:
```toml
[timeouts]
"io.containerd.timeout.shim.cleanup" = 5
"io.containerd.timeout.shim.load" = 5
"io.containerd.timeout.shim.shutdown" = 3
"io.containerd.timeout.task.state" = 2
```
Timeouts in the config are specified in seconds.
Timeouts are very hard to get right and giving this power to the user to
configure things is a huge improvement. Machines can be faster and
slower and depending on the CPU or load of the machine, a timeout may
need to be adjusted.
Signed-off-by: Michael Crosby <crosbymichael@gmail.com>
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