chore: fix generate-showcase script to checkout sdk-platform-java at …

…tag (GoogleCloudPlatform#2014)

* Add check and correction to checkout sdk-platform-java at version tag
* Add flag to exit script on error
* Remove command to locally install sdk-platform-java modules (other than showcase) from root

spring-cloud-generator/scripts/generate-showcase.sh

@@ -1,4 +1,5 @@
 #!/bin/bash
+set -e
 
 # To VERIFY: ./scripts/generate-showcase.sh
 # To UPDATE: /scripts/generate-showcase.sh -u
@@ -56,12 +57,16 @@ function generate_showcase_spring_starter(){
   cd ${SPRING_GENERATOR_DIR}
   GAPIC_GENERATOR_JAVA_VERSION=$(mvn help:evaluate -Dexpression=gapic-generator-java-bom.version -q -DforceStdout)
 
+  if [[ -z "$GAPIC_GENERATOR_JAVA_VERSION" ]]; then
+    echo "Missing sdk-platform-java commitish to checkout"
+    exit 1
+  fi
+
   # Clone sdk-platform-java (with showcase library)
   git clone https://github.com/googleapis/sdk-platform-java.git
-  git checkout "v${GAPIC_GENERATOR_JAVA_VERSION}"
+  cd sdk-platform-java && git checkout "v${GAPIC_GENERATOR_JAVA_VERSION}"
 
   # Install showcase client libraries locally
-  cd sdk-platform-java && mvn clean install -B -ntp -DskipTests -Dclirr.skip -Dcheckstyle.skip
   cd showcase && mvn clean install
   GAPIC_SHOWCASE_CLIENT_VERSION=$(mvn help:evaluate -Dexpression=project.version -q -DforceStdout)