Allow changing of distro at build time (#233)

* Allow changing of distro at build time

Ubuntu focal has better arm64 support for example.

* Document build-arg usage

* increase sleep time

as per https://github.com/kartoza/docker-postgis/pull/233#discussion_r409846863

Dockerfile

@@ -1,7 +1,8 @@
 #--------- Generic stuff all our Dockerfiles should start with so we get caching ------------
+ARG DISTRO=debian
 ARG IMAGE_VERSION=buster
 ARG IMAGE_VARIANT=-slim
-FROM debian:$IMAGE_VERSION$IMAGE_VARIANT
+FROM $DISTRO:$IMAGE_VERSION$IMAGE_VARIANT
 MAINTAINER Tim Sutton<tim@kartoza.com>
 
 # Reset ARG for version

README.md

@@ -80,6 +80,17 @@ Now edit ``71-apt-cacher-ng`` then do:
 docker build -t kartoza/postgis .
 ```
 
+### Building with alternative base distributions
+
+There are build args for `DISTRO` (=debian), `IMAGE_VERSION` (=buster)
+and `IMAGE_VARIANT` (=slim) which can be used to control the base image used
+(but it still needs to be Debian based and have PostgreSQL official apt repo).
+
+For example making Ubuntu 20.04 based build (for better arm64 support)
+```
+docker build --build-arg DISTRO=ubuntu --build-arg IMAGE_VERSION=focal --build-arg IMAGE_VARIANT="" -t kartoza/postgis .
+```
+
 ## Run
 
 

scenario_tests/datadir_init/test.sh

@@ -8,7 +8,7 @@ source ../test-env.sh
 # Run service
 docker-compose up -d
 
-sleep 5
+sleep 30
 
 services=("pg-default" "pg-new" "pg-recreate")