In e8786d73bb the logwrite package will
automatically append .log to every log.
In 5201049f2c the init package will send
stderr of a service `s` to a log named `s` and the stdout to `s.out`.
Therefore the files we create on disk are `s.log` and `s.out.log`.
This patch modifies the memlogd `logwrite` command-line wrapper to use
the same convention.
Note there is a confusing name clash between `pkg/logwrite` and `cmd/logwrite`
in `memlogd` modified here.
Signed-off-by: David Scott <dave.scott@docker.com>