Add CI job to build GParted on Ubuntu (!4)

Closes !4 - Add GitLab CI jobs to build and test GParted

.gitlab-ci.yml

@@ -11,6 +11,15 @@ stages:
                      gcc-c++ libuuid-devel parted-devel gtkmm24-devel make
                      polkit file
 
+.ubuntu_image_template: &ubuntu_image_definition
+  # Use official Ubuntu image https://hub.docker.com/_/ubuntu/.
+  image: ubuntu:latest
+  before_script:
+    - apt-get update
+    - apt-get install -y gnome-common gnome-doc-utils libglib2.0-dev-bin
+                         uuid-dev libparted-dev libgtkmm-2.4-dev make
+                         policykit-1
+
 .build_stage_template: &build_stage_definition
   stage: build
   script:
@@ -28,11 +37,15 @@ stages:
     - make check
     - make distcheck
 
-# Check GParted can be built and installed.
+# Check GParted can be built and installed on CentOS and Ubuntu.
 centos_build:
   <<: *centos_image_definition
   <<: *build_stage_definition
 
+ubuntu_build:
+  <<: *ubuntu_image_definition
+  <<: *build_stage_definition
+
 # Check GParted unit tests and distcheck pass.
 centos_test:
   <<: *centos_image_definition