Polishing.

Extract docker credentials into properties file.

See #339

Author: mp911de

Jenkinsfile

@@ -34,7 +34,7 @@ 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 clean dependency:list test -Dsort -U -B'
 						}
@@ -61,7 +61,7 @@ pipeline {
 					}
 					steps {
 						script {
-							docker.withRegistry('', 'hub.docker.com-springbuildmaster') {
+							docker.withRegistry(p['docker.registry'], p['docker.credentials']) {
 								docker.image(p['docker.java.next.image']).inside(p['docker.java.inside.basic']) {
 									sh 'MAVEN_OPTS="-Duser.name=jenkins -Duser.home=/tmp/jenkins-home" ./mvnw -s settings.xml -Pjava11 clean dependency:list test -Dsort -U -B'
 								}
@@ -80,7 +80,7 @@ pipeline {
 					}
 					steps {
 						script {
-							docker.withRegistry('', 'hub.docker.com-springbuildmaster') {
+							docker.withRegistry(p['docker.registry'], p['docker.credentials']) {
 								docker.image(p['docker.java.15.image']).inside(p['docker.java.inside.basic']) {
 									sh 'MAVEN_OPTS="-Duser.name=jenkins -Duser.home=/tmp/jenkins-home" ./mvnw -s settings.xml -Pjava11 clean dependency:list test -Dsort -U -B'
 								}
@@ -109,7 +109,7 @@ 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 ' +
 									'-Dartifactory.server=https://repo.spring.io ' +
@@ -139,7 +139,7 @@ pipeline {
 
 			steps {
 				script {
-					docker.withRegistry('', 'hub.docker.com-springbuildmaster') {
+					docker.withRegistry(p['docker.registry'], p['docker.credentials']) {
 						docker.image('adoptopenjdk/openjdk8:latest').inside('-v $HOME:/tmp/jenkins-home') {
 							sh 'MAVEN_OPTS="-Duser.name=jenkins -Duser.home=/tmp/jenkins-home" ./mvnw -s settings.xml -Pci,distribute ' +
 									'-Dartifactory.server=https://repo.spring.io ' +