STANBOL-1128: fixed a bug where deactivating the engine while FST structures where currently build where closing low level Solr streams. The Issues was actually the ExecutorService#shutdownNow() where interupting worker threads and FileChannels (as used by Solr) do get closed if either the producing or receiving thread get interupted (for security reasons). The new implemetnation does not use shutdownNow, but only uses shutdown(). The FstCreationTask now knows if creation tasks where cancelled and does not start (of if already started does ignore the result). Currently executed FST creation tasks can not be cancelled and will run until completed.

git-svn-id: https://svn.apache.org/repos/asf/stanbol/trunk@1517487 13f79535-47bb-0310-9956-ffa450edef68