kola-azure: add azure_managed_identity to jenkins

With the new argument which was added to cosa load the
AZURE_MANAGED_IDENTITY from openshift secrets.

ref: coreos/coreos-assembler#4223

Author: prestist

jobs/kola-azure.Jenkinsfile

@@ -88,8 +88,10 @@ cosaPod(memory: "${cosa_memory_request_mb}Mi", kvm: false,
             }
         }
 
-        withCredentials([file(variable: 'AZURE_KOLA_TESTS_CONFIG',
-                              credentialsId: 'azure-kola-tests-config')]) {
+        withCredentials([
+                file(variable: 'AZURE_KOLA_TESTS_CONFIG', credentialsId: 'azure-kola-tests-config'),
+                string(variable: 'AZURE_KOLA_MANAGED_IDENTITY', credentialsId: 'azure-kola-managed-identity')
+            ]) {
 
             def azure_testing_resource_group = pipecfg.clouds?.azure?.test_resource_group
             def azure_testing_storage_account = pipecfg.clouds?.azure?.test_storage_account
@@ -149,6 +151,7 @@ cosaPod(memory: "${cosa_memory_request_mb}Mi", kvm: false,
                      platformArgs: """-p=azure                               \
                          --azure-credentials \${AZURE_KOLA_TESTS_CONFIG}     \
                          --azure-location $region                            \
+                         --azure-managed-identity \${AZURE_KOLA_MANAGED_IDENTITY}   \
                          --azure-disk-uri /subscriptions/${azure_subscription}/resourceGroups/${azure_testing_resource_group}/providers/Microsoft.Compute/galleries/${azure_testing_gallery}/images/${azure_image_name}/versions/1.0.0""")
             } finally {
                 parallel "Delete Image": {