QPID-5671: [linearstore] Add ability to use disk partitions and select per-queue EFPs. This is the first part of resolving this issue and changes the journal directory structure to use symlinks instead of moving the actual files. This opens the way to having files from multiple partitions in the same journal. Other small improvements and tidy-ups also included.

git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk@1636598 13f79535-47bb-0310-9956-ffa450edef68