Implement restart-policy handling. Closes #1734

Applications without a restart-policy will have their policies set to `on-failure:10`. Users can completely unset the restart-policy using the `docker-options` plugin, though this will be equivalent to setting it explicitly to `no`.

Restart policies must be explicitly set, and the following are all valid:

- no
- unless-stopped
- always
- on-failure
- on-failure:NUMBER

plugins/ps/post-create

@@ -0,0 +1,14 @@
+#!/usr/bin/env bash
+set -eo pipefail; [[ $DOKKU_TRACE ]] && set -x
+source "$PLUGIN_CORE_AVAILABLE_PATH/common/functions"
+source "$PLUGIN_AVAILABLE_PATH/docker-options/functions"
+source "$PLUGIN_AVAILABLE_PATH/ps/functions"
+
+ps_post_create() {
+  declare desc="ps post-stop plugin trigger"
+  local trigger="ps_post_stop"
+  local APP="$1"
+
+  local passed_phases=(deploy)
+  add_passed_docker_option passed_phases[@] "--restart=on-failure:10"
+}