CI: Fix missing script block in jenkinsfiles

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

tests/CI/gates.jenkinsfile

@@ -240,8 +240,10 @@ pipeline {
 	}
 	post {
 		cleanup {
-			if (env.CLEANUP_WS_GATES.toBoolean()) {
-				cleanWs deleteDirs: true, notFailBuild: false
+			script {
+				if (env.CLEANUP_WS_GATES.toBoolean()) {
+					cleanWs deleteDirs: true, notFailBuild: false
+				}
 			}
 		}
 		/*

tests/CI/periodics-daily.jenkinsfile

@@ -159,8 +159,10 @@ pipeline {
 	}
 	post {
 		cleanup {
-			if (env.CLEANUP_WS_DAILIES.toBoolean()) {
-				cleanWs deleteDirs: true, notFailBuild: false
+			script {
+				if (env.CLEANUP_WS_DAILIES.toBoolean()) {
+					cleanWs deleteDirs: true, notFailBuild: false
+				}
 			}
 		}
 		success {

tests/CI/ref_debug.jenkinsfile

@@ -129,8 +129,10 @@ pipeline {
 	}
 	post {
 		cleanup {
-			if (env.CLEANUP_WS_REF_DEBUG.toBoolean()) {
-				cleanWs deleteDirs: true, notFailBuild: false
+			script {
+				if (env.CLEANUP_WS_REF_DEBUG.toBoolean()) {
+					cleanWs deleteDirs: true, notFailBuild: false
+				}
 			}
 		}
 		success {