update upgrade test script to have --force flag and proper testing versions (istio#18570)

Author: carolynhu

prow/upgrade-tests.sh

@@ -28,13 +28,13 @@ WD=$(cd "$WD"; pwd)
 ROOT=$(dirname "$WD")
 
 # Set up inputs needed by /istio/istio/tests/upgrade/test_crossgrade.sh, the default settings is to test upgrade from
-# 1.3.1 to 1.3.2 using helm chart
+# 1.3.0 to 1.3.4 using helm chart
 # These environment variables are passed by /istio/test-infra/prow/cluster/jobs istio periodic upgrade jobs
 export SOURCE_HUB=${SOURCE_HUB:-"docker.io/istio"}
-export SOURCE_TAG=${SOURCE_TAG:-"1.3.1"}
+export SOURCE_TAG=${SOURCE_TAG:-"1.3.0"}
 export SOURCE_RELEASE_PATH=${SOURCE_RELEASE_PATH:-"https://github.com/istio/istio/releases/download/${SOURCE_TAG}"}
 export TARGET_HUB=${TARGET_HUB:-"docker.io/istio"}
-export TARGET_TAG=${TARGET_TAG:-"1.3.2"}
+export TARGET_TAG=${TARGET_TAG:-"1.3.4"}
 export TARGET_RELEASE_PATH=${TAGET_RELEASE_PATH:-"https://github.com/istio/istio/releases/download/${TARGET_TAG}"}
 export INSTALL_OPTIONS=${ISTALL_OPTIONS:-"helm"}
 export FROM_PATH=${FROM_PATH:-"$(mktemp -d from_dir.XXXXXX)"}

tests/upgrade/test_crossgrade.sh

@@ -245,12 +245,17 @@ installIstioAtVersionUsingIstioctl(){
 }
 
 # istioctl x upgrade supports upgrade istio release version
-# from 1.3.x to 1.3.y
 # from 1.3.x to 1.4.0
+# 1.3.3 to 1.4.0
+# 1.3.0 to 1.4.0 --force
 upgradeIstioAtVersionUsingIstioctl(){
   writeMsg "istioctl upgrade istio using version ${2} from ${3}."
   istioctl_path="${3}"/bin
-  "${istioctl_path}"/istioctl experimental manifest upgrade --skip-confirmation
+  if "${FROM_TAG}" < "1.3.3"; then
+    "${istioctl_path}"/istioctl experimental manifest upgrade --skip-confirmation --force
+  else
+    "${istioctl_path}"/istioctl experimental manifest upgrade --skip-confirmation
+  fi
 }
 
 istioInstallOptions() {
@@ -494,7 +499,6 @@ resetConfigMap istio-sidecar-injector "${TMP_DIR}"/sidecar-injector-configmap.ya
 restartDataPlane echosrv-deployment-v1
 sleep 140
 
-
 istioInstallOptions
 waitForPodsReady "${ISTIO_NAMESPACE}"