chimera: refactor PGET into abstract node

Given the fact that we would like to optimize the size of the file handles on the ".(get)" operations by not including the arguments, it now makes no sense to have the FsInode_PGET represent any concrete operation. Instead, we would like a hierarchy of get operations which have the basic read mechanism in common.

This patch represents the first of a two part refactoring.  It does the following:

1.  Changes FsInode_PGET to an abstract node.
2.  Implements the degenerate case (cursor) as a separate subclass FsInode_PCUR.
3.  Changes FsInode_CRC (checksum) to be a subclass of PGET.
4.  Adjusts the FsInodeType to reflect these changes.
5.  Modifies the JdcbFs class accordingly.

Testing: Works on both nfs 3 and nfs v4.1.

Target: master
Request: 2.7
Patch: http://rb.dcache.org/r/6407
Require-book: no
Require-notes: no
Acked-by: Tigran

Changes are invisible to user.
(cherry picked from commit 5e38de989e7089ad16c67f8a36cd228804db8f66)

Signed-off-by: alrossi <arossi@otfrid.fnal.gov>
chimera: refactor PGET, part 2: eliminate caching of file locality node

Use of the Guava cache to maintain state on the FsInode used to convey locality information is unnecessary if the operation subclasses the abstract PGET operation.

The slight disadvantage is that a call to the PoolManager will be made each time stat() is called by the client; the advantage is that the server is not maintaining state on client operations, which does not really fit the NFS protocol and was something of a hack.

This patch completes the refactoring begun in 6407.  It changes the FsInode_PLOC to subclass PGET, removes the caching mechanism from the DCacheAware fs interface, and adds one method the FileSystem API (getFileLocality).

Testing: Tested successfully on nfs3 and nfs v4.1.

Target: master
Request: 2.7
Patch: http://rb.dcache.org/r/6409
Require-book: no
Require-notes: no
Depends-on: http://rb.dcache.org/r/6407
Acked-by: Tigran

Changes are invisible to the user.
(cherry picked from commit cf963c4a6a78cc92d27209512be98fdc047e6b33)

Signed-off-by: alrossi <arossi@otfrid.fnal.gov>
Merge pull request #388 from alrossi/fix/2.7/refactor_chimera_pget

Fix/2.7/refactor chimera pget