Critical Description
Recently pre-commit builds seems run some commands twice. For example, in console of https://builds.apache.org/job/PreCommit-HBASE-Build/975/console (HBASE-15325) or https://builds.apache.org/job/PreCommit-HBASE-Build/978/console (HBASE-15406), we run "Patch findbugs detection", "Patch javadoc verification", "Running unit tests" twice for each task. HadoopQA also comment repeated results with different runtime in JIRA. (See this comment: https://issues.apache.org/jira/browse/HBASE-15325?focusedCommentId=15195199&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-15195199 )
We will run tests of hbase-server for four times, twice on jdk7 and twice on jdk8, it will be very slow...