Add "showAllOutput" project property

Added a property to show all test output, useful for debugging.

Usage: ./gradlew -PshowAllOutput=true build
Tested:
  Verified that the property does the right thing for true and false values
  and verified that the build doesn't show test output if it's omitted.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=225854375

gradle/build.gradle

@@ -20,6 +20,13 @@ plugins {
   id 'com.bmuschko.docker-java-application' version '4.0.4' apply false
 }
 
+// Provide defaults for all of the project properties.
+
+// showAllOutput: boolean.  If true, dump all test output during the build.
+if (!project.hasProperty('showAllOutput')) {
+  ext.showAllOutput = 'false'
+}
+
 // Only do linting if the build is successful.
 gradleLint.autoLintAfterFailure = false
 
@@ -245,6 +252,10 @@ subprojects {
     }
   }
 
+  test {
+      testLogging.showStandardStreams = Boolean.parseBoolean(showAllOutput)
+  }
+
   if (project.name == 'core') return
 
   ext.relativePath = "google/registry/${project.name}"