build: move common parts out from this project

Per discussion in PR #138 and some private discussion with
@omron93:  We keep the "warning" Makefile-hack to inform users who
have old clones of this repository and will do "git pull" (those
users must explicitly init the git module).

.gitmodules

@@ -0,0 +1,3 @@
+[submodule "common"]
+	path = common
+	url = https://github.com/sclorg/container-common-scripts.git

Makefile

@@ -1,7 +1,10 @@
-# Variables are documented in hack/build.sh.
+# Variables are documented in common/build.sh.
 BASE_IMAGE_NAME = postgresql
 VERSIONS = 9.4 9.5
 OPENSHIFT_NAMESPACES = 9.2
 
-# Include common Makefile code.
-include hack/common.mk
+# HACK:  Ensure that 'git pull' for old clones doesn't cause confusion.
+# New clones should use '--recursive'.
+.PHONY: $(shell test -f common/common.mk || echo >&2 'Please do "git submodule update --init" first.')
+
+include common/common.mk

README.md

@@ -30,7 +30,7 @@ Choose either the CentOS7 or RHEL7 based image:
     subscribed RHEL machine.
 
     ```
-    $ git clone https://github.com/openshift/postgresql.git
+    $ git clone --recursive https://github.com/sclorg/postgresql-container.git
     $ cd postgresql
     $ make build TARGET=rhel7 VERSION=9.5
     ```
@@ -46,7 +46,7 @@ Choose either the CentOS7 or RHEL7 based image:
     To build a PostgreSQL image from scratch run:
 
     ```
-    $ git clone https://github.com/openshift/postgresql.git
+    $ git clone --recursive https://github.com/sclorg/postgresql-container.git
     $ cd postgresql
     $ make build TARGET=centos7 VERSION=9.5
     ```