In cases where a logging plugin has crashed when the daemon tries to
copy the container stdio to the logging plugin it returns a broken pipe
error and any log entries that occurr while the plugin is down are lost.
Fix this by opening read+write in the daemon so logs are not lost while
the plugin is down.
Signed-off-by: Brian Goff <cpuguy83@gmail.com>
Logging plugins use the same HTTP interface as other plugins for basic
command operations meanwhile actual logging operations are handled (on
Unix) via a fifo.
The plugin interface looks like so:
```go
type loggingPlugin interface {
StartLogging(fifoPath string, loggingContext Context) error
StopLogging(fifoPath)
```
This means a plugin must implement `LoggingDriver.StartLogging` and
`LoggingDriver.StopLogging` endpoints and be able to consume the passed
in fifo.
Logs are sent via stream encoder to the fifo encoded with protobuf.
Signed-off-by: Brian Goff <cpuguy83@gmail.com>
