MINOR: Upgrade gradle to 6.8 and test retry plugin to 1.2.0 (#9849)

Also fix generation of `gradlew` when `APP_HOME` contains a directory with spaces
in its name.

Release notes:
* https://docs.gradle.org/6.8/release-notes.html
* https://github.com/gradle/test-retry-gradle-plugin/releases/tag/v1.2.0

In addition to existing tests, verified that `./gradlewAll jar` succeeds.

Reviewers: Chia-Ping Tsai <chia7712@gmail.com>

gradle/dependencies.gradle

@@ -61,7 +61,7 @@ versions += [
   bcpkix: "1.66",
   checkstyle: "8.20",
   commonsCli: "1.4",
-  gradle: "6.7.1",
+  gradle: "6.8",
   gradleVersionsPlugin: "0.36.0",
   grgit: "4.1.0",
   httpclient: "4.5.12",
@@ -115,7 +115,7 @@ versions += [
   spotbugs: "4.1.4",
   spotbugsPlugin: "4.6.0",
   spotlessPlugin: "5.8.2",
-  testRetryPlugin: "1.1.9",
+  testRetryPlugin: "1.2.0",
   zinc: "1.3.5",
   zookeeper: "3.5.8",
   zstd: "1.4.5-12"

gradle/wrapper/gradle-wrapper.properties

@@ -1,5 +1,5 @@
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-6.7.1-all.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-6.8-all.zip
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists

gradlew

@@ -83,8 +83,8 @@ esac
 
 # Loop in case we encounter an error.
 for attempt in 1 2 3; do
-  if [ ! -e "$APP_HOME"/gradle/wrapper/gradle-wrapper.jar ]; then
+  if [ ! -e "$APP_HOME/gradle/wrapper/gradle-wrapper.jar" ]; then
-    if ! curl -s -S --retry 3 -L -o "$APP_HOME/gradle/wrapper/gradle-wrapper.jar" "https://raw.githubusercontent.com/gradle/gradle/v6.7.1/gradle/wrapper/gradle-wrapper.jar"; then
+    if ! curl -s -S --retry 3 -L -o "$APP_HOME/gradle/wrapper/gradle-wrapper.jar" "https://raw.githubusercontent.com/gradle/gradle/v6.8.0/gradle/wrapper/gradle-wrapper.jar"; then
       rm -f "$APP_HOME/gradle/wrapper/gradle-wrapper.jar"
       # Pause for a bit before looping in case the server throttled us.
       sleep 5

wrapper.gradle

@@ -49,7 +49,7 @@ task bootstrapWrapper() {
         def bootstrapString = """
       # Loop in case we encounter an error.
       for attempt in 1 2 3; do
-        if [ ! -e $wrapperJarPath ]; then
+        if [ ! -e "$wrapperJarPath" ]; then
           if ! curl -s -S --retry 3 -L -o "$wrapperJarPath" "$wrapperJarUrl"; then
             rm -f "$wrapperJarPath"
             # Pause for a bit before looping in case the server throttled us.