[gparted] Parameterise CI config ready for also using a Ubuntu image (!4)

[Curtis Gedak <gedakc src gnome org>]

commit eb2435231bb32e44d1b42891bd248fda0e747077
Author: Mike Fleetwood <mike fleetwood googlemail com>
Date:   Sat Jun 23 13:28:57 2018 +0100

    Parameterise CI config ready for also using a Ubuntu image (!4)
    
    Prepare the GitLab Continuous Integration configuration for also
    building and testing GParted on a Ubuntu image.  The definition of the
    image and before_script, which so far specify the CentOS Docker image
    and how to install the required RPM packages, need to move from being
    top level nodes to being defined per job.  Namely within jobs
    'centos_build' and 'centos_test'.
    
    To avoid duplicating various nodes within multiple jobs, YAML anchors
    (&LABEL) and references (*LABEL) are used.  They are defined in ignored
    jobs, job names starting with a dot (.).
    
    Closes !4 - Add GitLab CI jobs to build and test GParted

 .gitlab-ci.yml | 34 +++++++++++++++++++++-------------
 1 file changed, 21 insertions(+), 13 deletions(-)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 6597791c..be0dd902 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -1,26 +1,24 @@
-# Use official CentOS image https://hub.docker.com/_/centos/.
-image: centos:latest
-
-before_script:
-  - yum update -y
-  - yum install -y which gnome-common gnome-doc-utils glib2-devel intltool
-                   gcc-c++ libuuid-devel parted-devel gtkmm24-devel make
-                   polkit file
-
 stages:
   - build
   - test
 
-# Check GParted can be built and installed.
-centos_build:
+.centos_image_template: &centos_image_definition
+  # Use official CentOS image https://hub.docker.com/_/centos/.
+  image: centos:latest
+  before_script:
+    - yum update -y
+    - yum install -y which gnome-common gnome-doc-utils glib2-devel intltool
+                     gcc-c++ libuuid-devel parted-devel gtkmm24-devel make
+                     polkit file
+
+.build_stage_template: &build_stage_definition
   stage: build
   script:
     - ./autogen.sh
     - make
     - make install
 
-# Check GParted unit tests and distcheck pass.
-centos_test:
+.test_stage_template: &test_stage_definition
   stage: test
   script:
     - ./autogen.sh
@@ -29,3 +27,13 @@ centos_test:
     - export GTEST_FILTER='-BlockSpecialTest.NamedBlockSpecialObjectBySymlinkMatches'
     - make check
     - make distcheck
+
+# Check GParted can be built and installed.
+centos_build:
+  <<: *centos_image_definition
+  <<: *build_stage_definition
+
+# Check GParted unit tests and distcheck pass.
+centos_test:
+  <<: *centos_image_definition
+  <<: *test_stage_definition