[CI] Add var for run bm_core on release branch

Task: https://mirantis.jira.com/browse/PRODX-39216

Change-Id: I48ff0a58aaa4ff154f00d5342df9e983469f661c
diff --git a/src/com/mirantis/mk/KaasUtils.groovy b/src/com/mirantis/mk/KaasUtils.groovy
index e3c2ddd..1955288 100644
--- a/src/com/mirantis/mk/KaasUtils.groovy
+++ b/src/com/mirantis/mk/KaasUtils.groovy
@@ -118,7 +118,7 @@
     def enableVsphereDemo = true
     def enableOSDemo = true
     def enableBMDemo = true
-    def enablebmCoreDemo = false
+    def enablebmCoreDemo = env.ALLOW_BM_CORE_ON_DEMAND ? env.ALLOW_BM_CORE_ON_DEMAND.toBoolean() : false
     def bmCoreCleanup = env.BM_CORE_CLEANUP ? env.BM_CORE_CLEANUP : true
     def enableArtifactsBuild = true
     def bmDeployType = 'virtual'