LU-680 lfs: instance <-> mount point mapping from lfs

A new option to 'lfs' has been created to return the mapping
between Lustre filesystem instance and paths. The option
is 'getname' and it may be called with or without arguements.

'lfs getname' without arguments returns the instances of all
Lustre mount points.

'lfs getname [path...]' returns the instance of each specified
path. If the path is not a Lustre instance 'No such device' is
returned.

OBD_IOC_GETNAME has been added to file.c to provide consistent
behavior for file as well as directory paths.

A llapi_getname helper function has been added to liblustreapi
that returns a lustre instance name if a path is provided.

Documentation for 'lfs getname' is included inline an the lfs
man page has been updated.

Signed-off-by: Richard Henwood <rhenwood@whamcloud.com>
Signed-off-by: John L. Hammond <jhammond@tacc.utexas.edu>
Change-Id: Iab8ff12d604c7ce853f3c204b455e3b641f659f4
Reviewed-on: http://review.whamcloud.com/1373
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>