Add intial test .gitlab-ci.yml

.gitlab-ci.yml

+variables:
+  MAVEN_OPTS: "-Dmaven.repo.local=.m2/repository -Dorg.slf4j.simpleLogger.log.org.apache.maven.cli.transfer.Slf4jMavenTransferListener=WARN -Dorg.slf4j.simpleLogger.showDateTime=true -Djava.awt.headless=true"
+  MAVEN_CLI_OPTS: "--batch-mode --errors --fail-at-end --show-version -DinstallAtEnd=true -DdeployAtEnd=true"
+
+cache:
+  paths:
+    - .m2/repository
+
+.validate: &validate
+  stage: build
+  script:
+    - 'mvn $MAVEN_CLI_OPTS test-compile'
+
+.verify: &verify
+  stage: test
+  script:
+    - 'mvn $MAVEN_CLI_OPTS verify site site:stage'
+  except:
+    - master
+
+# Validate merge requests using JDK8
+validate:jdk8:
+  <<: *validate
+  image: maven:3.3.9-jdk-8
+
+# Verify merge requests using JDK8
+verify:jdk8:
+  <<: *verify
+  image: maven:3.3.9-jdk-8