Redesign integration testing to copy images to nested containers

Previously, the strategy for avoiding lots of rebuilding and repulling
for each Docker version being tested was to use a mountpoint to persist
/var/lib/docker. This was pretty broken, and may not be a reliable
strategy. This commit changes the scripts to instead build/pull images
outside the innermost container, and copy them to the final test
environment with docker save/docker load.

This requires a fair amount of changes, since run.sh must now
communicate with the Docker engine that was formerly started by
test_runner.sh. The code that starts this engine has been broken out to
run_engine.sh so that starting the engine and running the tests under it
can be done separately (with the images loaded in between these steps).

Signed-off-by: Aaron Lehmann <aaron.lehmann@docker.com>

contrib/docker-integration/run_engine.sh

@@ -0,0 +1,12 @@
+#!/bin/sh
+set -e
+set -x
+
+# Set IP address in /etc/hosts for localregistry
+IP=$(ifconfig eth0|grep "inet addr:"| cut -d: -f2 | awk '{ print $1}')
+echo "$IP localregistry" >> /etc/hosts
+
+sh install_certs.sh localregistry
+
+docker --daemon -H "0.0.0.0:$ENGINE_PORT" --log-level=panic \
+	--storage-driver="$DOCKER_GRAPHDRIVER" --exec-driver="$EXEC_DRIVER"