Add pkg/logwrite which writes and rotates log files

This process connects to memlogd and streams logs to individual files,
one per log. It keeps track of how many bytes have been written to each
file and rotates when the file size exceeds a defined threshold.

By default the maximum size of each file before rotation is 1MiB and
we keep up to 10 files per log.

Signed-off-by: David Scott <dave.scott@docker.com>

examples/logging.yml

@@ -24,6 +24,8 @@ services:
   - name: write-to-the-logs
     image: alpine
     command: ["/bin/sh", "-c", "while /bin/true; do echo hello $(date); sleep 1; done" ]
+  - name: write-and-rotate-logs
+    image: linuxkit/logwrite:7859c102a963828fd9c5aa3837db9600483220c7
 trust:
   org:
     - linuxkit