install: Improve support for non-default puppet rules.

Previously, the install script would fail if you passed various
non-default puppet rules, since the code to configure and restart
services that runs later on in the install script largely ran
unconditionally, regardless of whether the relevant service was
actually installed on the target system.

This should make the main install script reusable for installing
e.g. a dedicated Postgres server for use with Zulip.

scripts/lib/install

@@ -49,25 +49,36 @@ mkdir -p /etc/zulip
 echo -e "[machine]\npuppet_classes = $PUPPET_CLASSES\ndeploy_type = $DEPLOYMENT_TYPE" > /etc/zulip/zulip.conf
 /root/zulip/scripts/zulip-puppet-apply -f
 
+# Detect which features were selected for the below
+[ -e "/etc/init.d/camo" ]; has_camo=$?
+[ -e "/etc/init.d/nginx" ]; has_nginx=$?
+[ -e "/etc/supervisor/conf.d/zulip.conf" ]; has_appserver=$?
+[ -e "/etc/cron.d/rabbitmq-numconsumers" ]; has_rabbit=$?
+[ -e "/etc/init.d/postgresql" ]; has_postgres=$?
+
 # These server restarting bits should be moveable into puppet-land, ideally
 apt-get -y upgrade
-if [ -e "/etc/init.d/nginx" ]; then
+
+if [ "$has_nginx" = 0 ]; then
     # Check nginx was configured properly now that we've installed it.
     # Most common failure mode is certs not having been installed.
     nginx -t
     service nginx restart
 fi
 
+if [ "$has_appserver" = 0 ]; then
     /root/zulip/scripts/setup/generate_secrets.py
     cp -a /root/zulip/zproject/local_settings_template.py /etc/zulip/settings.py
     ln -nsf /etc/zulip/settings.py /root/zulip/zproject/local_settings.py
+fi
 
 # Restart camo since generate_secrets.py likely replaced its secret key
-if [ -z "$TRAVIS" ]; then
+if [ "$has_camo" = 0 ] && [ -z "$TRAVIS" ]; then
     # We don't run this in Travis CI due to a weird hang bug
     service camo restart
 fi
 
+if [ "$has_rabbit" = 0 ]; then
     if ! rabbitmqctl status >/dev/null; then
         set +x
         echo; echo "RabbitMQ seems to not have started properly after the installation process."
@@ -78,11 +89,14 @@ if ! rabbitmqctl status >/dev/null; then
         set -x
         exit 1
     fi
-
     /root/zulip/scripts/setup/configure-rabbitmq
+fi
 
+if [ "$has_postgres" = 0 ]; then
     /root/zulip/scripts/setup/postgres-init-db
+fi
 
+if [ "$has_appserver" = 0 ]; then
     deploy_path=$(/root/zulip/zulip_tools.py make_deploy_path)
     mv /root/zulip "$deploy_path"
     ln -nsf /home/zulip/deployments/next /root/zulip
@@ -92,6 +106,8 @@ ln -nsf /etc/zulip/settings.py "$deploy_path"/zproject/local_settings.py
     mkdir -p "$deploy_path"/prod-static/serve
     cp -rT "$deploy_path"/prod-static/serve /home/zulip/prod-static
     chown -R zulip:zulip /home/zulip /var/log/zulip /etc/zulip/settings.py
+fi
+
 if [ -e "/var/run/supervisor.sock" ]; then
     # If supervisor isn't running, no need to chown its socket
     chown zulip:zulip /var/run/supervisor.sock