Bug 1165229 - Heroku: Move the deploy tasks to their own script

Since we'll soon be adding reporting deploys to New Relic, which will be
too verbose to include in the Procfile. Also adds additional log output
(which follows the buildpack compile log formatting convention) to make
it easier to find & follow the release tasks on Papertrail.

Uses the `set -euo pipefail` recommendation from:
http://redsymbol.net/articles/unofficial-bash-strict-mode/

Procfile

@@ -7,4 +7,5 @@ worker_buildapi_4hr: newrelic-admin run-program celery -A treeherder worker -Q b
 worker_default: newrelic-admin run-program celery -A treeherder worker -Q default,cycle_data,calculate_durations,fetch_bugs,fetch_allthethings,generate_perf_alerts,detect_intermittents --maxtasksperchild=50 --concurrency=3
 worker_hp: newrelic-admin run-program celery -A treeherder worker -Q classification_mirroring,publish_to_pulse --maxtasksperchild=50 --concurrency=1
 worker_log_parser: newrelic-admin run-program celery -A treeherder worker -Q log_parser_fail,log_parser,log_parser_hp,log_parser_json,error_summary,store_error_summary,autoclassify --maxtasksperchild=50 --concurrency=5
-release: ./manage.py migrate --noinput && ./manage.py load_initial_data && ./manage.py init_datasources
+
+release: ./bin/pre_deploy

bin/pre_deploy

@@ -0,0 +1,16 @@
+#!/usr/bin/env bash
+# Tasks run after the Heroku buildpack compile, but prior to the deploy.
+# If failures occur, the deploy will not proceed.
+
+set -euo pipefail
+
+echo "-----> PRE-DEPLOY: Running Django migration..."
+./manage.py migrate --noinput
+
+echo "-----> PRE-DEPLOY: Loading initial data..."
+./manage.py load_initial_data
+
+echo "-----> PRE-DEPLOY: Initialising datasources..."
+./manage.py init_datasources
+
+echo "-----> PRE-DEPLOY: Complete!"