centralPipelineLoad step

A more convenient way to checkout the project sources. The idea is to
have a Jenkinsfile in the payload repository that only loads the shared
library and then runs this step. This step in turn loads a Jenkinsfile
from another repository.
The repo url, branch, Jenkinsfile path and credentials ID can be
provided to the step. The Jenkinsfile is first checked out to a
temporary folder, before it is loaded.
The payload repo must include a Jenkinsfile to be loaded with this
approach.

vars/centralPipelineLoad.groovy

@@ -0,0 +1,45 @@
+import com.sap.piper.Utils
+
+/**
+ * centralPipelineLoad
+ * Load a central pipeline.
+ *
+ */
+def call(Map parameters = [:]) {
+
+    handlePipelineStepErrors (stepName: 'centralPipelineLoad', stepParameters: parameters) {
+
+        def utils = new Utils()
+
+        // The coordinates of the central pipeline script
+        def repo = utils.getMandatoryParameter(parameters, 'repoUrl', null)
+        def branch = utils.getMandatoryParameter(parameters, 'branch', 'master')
+        def path = utils.getMandatoryParameter(parameters, 'jenkinsfilePath', 'Jenkinsfile')
+
+        // In case access to the repository containing the central pipeline
+        // script is restricted the credentialsId of the credentials used for
+        // accessing the repository needs to be provided below. The corresponding
+        // credentials needs to be configured in Jenkins accordingly.
+        def credentialsId = utils.getMandatoryParameter(parameters, 'credentialsId', '')
+
+        // temporary folder used for storing the central jenkins file locally.
+        def temporaryPipelineFolder = "pipeline-${UUID.randomUUID().toString()}"
+
+        deleteDir()
+        dir(temporaryPipelineFolder) {
+
+            checkout([$class: 'GitSCM', branches: [[name: branch]],
+                      doGenerateSubmoduleConfigurations: false,
+                      extensions: [[$class: 'SparseCheckoutPaths',
+                                    sparseCheckoutPaths: [[path: path]]
+                                   ]],
+                      submoduleCfg: [],
+                      userRemoteConfigs: [[credentialsId: credentialsId,
+                                           url: repo
+                                          ]]
+            ])
+        }
+
+        load "${temporaryPipelineFolder}/${path}"
+    }
+}