update postgis whenever using a postgres docker image for jenkins

This might help mitigate the dreaded postgis error we've been seeing
(OperationalError: could not access file "$libdir/postgis-X.X) while
allowing us to continue to use our docker volume caching mechanism
in jenkins

Change-Id: I9ae8f660709ce4e261ac064ce294740264166882
Reviewed-on: https://gerrit.instructure.com/133015
Reviewed-by: Simon Williams <simon@instructure.com>
Tested-by: Jenkins
Product-Review: Shahbaz Javeed <sjaveed@instructure.com>
QA-Review: Shahbaz Javeed <sjaveed@instructure.com>

build/docker-compose/postgres/9.5/Dockerfile

@@ -8,6 +8,5 @@ RUN echo "max_locks_per_transaction = 640" >> /usr/share/postgresql/$PG_MAJOR/po
 
 # needs to be named .sh for it to get run
 COPY /create-dbs.sh /docker-entrypoint-initdb.d/
-COPY /zz-run-update-postgis.sh /docker-entrypoint-initdb.d/
 
 COPY /wait-for-it /

build/docker-compose/postgres/9.5/zz-run-update-postgis.sh

@@ -1,4 +0,0 @@
-#!/usr/bin/env bash
-
-export POSTGRES_USER=postgres
-/usr/local/bin/update-postgis.sh

build/docker_composer.rb

@@ -111,6 +111,7 @@ class DockerComposer
       docker_compose "build #{services.join(" ")}"
       prepare_volumes
       start_services
+      update_postgis
       db_prepare unless using_snapshot? # already set up, just need to migrate
     end
 
@@ -129,6 +130,15 @@ class DockerComposer
       wait_for "data_loader"
     end
 
+    # To prevent errors similar to: OperationalError: could not access file "$libdir/postgis-X.X
+    # These happen when your docker image expects one version of PostGIS but the volume has a different one.  This
+    # should noop if there's no mismatch in the version of PostGIS
+    # https://hub.docker.com/r/mdillon/postgis/
+    def update_postgis
+      puts "Updating PostGIS"
+      docker "exec --user postgres #{ENV["COMPOSE_PROJECT_NAME"]}_postgres_1 update-postgis.sh"
+    end
+
     def db_prepare
       # pg db setup happens in create-dbs.sh (when we docker-compose up),
       # but cassandra doesn't have a similar hook