CI: Fix missing script block in jenkinsfiles

Change-Id: I9f44a3d5085ea7880fad1a3883a4820907e29ea3
(cherry picked from commit 95213b01d2)

tests/CI/gates.jenkinsfile

@@ -240,10 +240,12 @@ pipeline {
 	}
 	post {
 		cleanup {
+			script {
 				if (env.CLEANUP_WS_GATES.toBoolean()) {
 					cleanWs deleteDirs: true, notFailBuild: false
 				}
 			}
+		}
 		/*
 		 * The Gerrit Trigger will automatically post the "Verified" results back
 		 * to Gerrit but the verification publisher publishes extra stuff in the

tests/CI/periodics-daily.jenkinsfile

@@ -159,10 +159,12 @@ pipeline {
 	}
 	post {
 		cleanup {
+			script {
 				if (env.CLEANUP_WS_DAILIES.toBoolean()) {
 					cleanWs deleteDirs: true, notFailBuild: false
 				}
 			}
+		}
 		success {
 			echo "Reporting ${currentBuild.currentResult} Passed"
 		}

tests/CI/ref_debug.jenkinsfile

@@ -129,10 +129,12 @@ pipeline {
 	}
 	post {
 		cleanup {
+			script {
 				if (env.CLEANUP_WS_REF_DEBUG.toBoolean()) {
 					cleanWs deleteDirs: true, notFailBuild: false
 				}
 			}
+		}
 		success {
 			echo "Reporting ${currentBuild.currentResult} Passed"
 		}