Polishing.

Extract docker credentials into properties file.

See #715

Author: mp911de

Jenkinsfile

@@ -38,7 +38,7 @@ pipeline {
 
 			steps {
 				script {
-					docker.withRegistry('', 'hub.docker.com-springbuildmaster') {
+					docker.withRegistry(p['docker.registry'], p['docker.credentials']) {
 						docker.image(p['docker.java.lts.image']).inside(p['docker.java.inside.docker']) {
 							sh "docker login --username ${DOCKER_HUB_USR} --password ${DOCKER_HUB_PSW}"
 							sh 'PROFILE=ci ci/test.sh'
@@ -68,7 +68,7 @@ pipeline {
 
 			steps {
 				script {
-					docker.withRegistry('', 'hub.docker.com-springbuildmaster') {
+					docker.withRegistry(p['docker.registry'], p['docker.credentials']) {
 						docker.image(p['docker.java.main.image']).inside(p['docker.java.inside.basic']) {
 							sh 'MAVEN_OPTS="-Duser.name=jenkins -Duser.home=/tmp/jenkins-home" ./mvnw -s settings.xml -Pci,artifactory -Dmaven.repo.local=/tmp/jenkins-home/.m2/spring-data-r2dbc-non-root ' +
 									'-Dartifactory.server=https://repo.spring.io ' +