using --noIndex hangs the indexer

[vladak]

As identified on #4373, running indexer with the --noIndex option causes it to hang. This is because of the changes in 2af6dbc. After these changes the IndexParallelizer is no longer bounced which results in a OpenGrok-ctags-watcher thread to stay around after main() is done. The thread appeared because ctags is run via validateUniversalCtags() in prepareIndexer().

[tarzanek]

@vladak you have a typo in patch 1ea5adf
"ctags" word got lost from
https://github.com/oracle/opengrok/blob/master/opengrok-indexer/src/main/java/org/opengrok/indexer/index/Indexer.java#L1055