Improve validation guide for the reproducible build step

Author: aherbert

src/main/resources/commons-xdoc-templates/vote-txt-template.txt

@@ -138,6 +138,8 @@ Linux: uname -a
 
 To check that a build is reproducible, run:
 
+# Verify using a JDK major version matching: @JAVA_VERSION@
+export TZ="@TIMEZONE@"
 mvn clean verify artifact:compare -DskipTests -Dreference.repo=https://repository.apache.org/content/repositories/staging/ '-Dbuildinfo.ignore=*/*.spdx.json'
 
 Note that this excludes SPDX files from the check.

src/main/scripts/generate-xdocs.build.xml

@@ -126,6 +126,8 @@
              <filter token="TAGCOMMIT"      value="${git.tag.commit}"/>
              <filter token="SITEURL"        value="${svn.site.url}"/>
              <filter token="NEXUS_REPO_ID"  value="${commons.nexus.repo.id}"/>
+             <filter token="JAVA_VERSION"   value="${java.version}"/>
+             <filter token="TIMEZONE"       value="${user.timezone}"/>
             </filterset>
         </copy>