Replace the version-specific Dockerfiles with one staged Dockerfile

script/cibuild

@@ -2,7 +2,9 @@
 
 set -e
 
-docker_compose="docker-compose --file test-envs/docker-compose-$1-$2.yml"
+export RUBY_VERSION=$1
+
+docker_compose="docker-compose --file test-envs/docker-compose-$2.yml"
 
 function cleanup() {
   $docker_compose down

script/poll-for-db

@@ -2,13 +2,15 @@
 
 echo "==> Polling DB…"
 
-appdir=$(cd $(dirname "$0")/.. && pwd)
-[ -f /etc/app-env ] || exec "$appdir/script/docker-environment" $0 $@
+if [ "$DATABASE_TYPE" == "mysql" ]; then
+  appdir=$(cd $(dirname "$0")/.. && pwd)
+  [ -f /etc/app-env ] || exec "$appdir/script/docker-environment" $0 $@
 
-for i in {1..60}; do
-  nc -z -w5 db 3306 && exit
-  sleep 1
-done
+  for i in {1..60}; do
+    nc -z -w5 db 3306 && exit
+    sleep 1
+  done
 
-echo "Unable to reach database!"
-exit 1
+  echo "Unable to reach database!"
+  exit 1
+fi