staging: lustre: lmv: separate master object with master stripe

Separate master stripe with master object, so
1. stripeEA only exists on master object.
2. sub-stripe object will be inserted into master object
as sub-directory, and it can get the master object by "..".

By this, it will remove those specilities for stripe0 in
LMV and LOD. And also simplify LFSCK, i.e. consistency check
would be easier.

When then master object becomes an orphan, we should
mark all of its sub-stripes as dead object as well,
otherwise client might still be able to create files
under these stripes.

A few fixes for striped directory layout lock:

 1. stripe 0 should be locked as EX, same as other stripes.
 2. Acquire the layout for directory, when it is being unliked.

Signed-off-by: wang di <di.wang@intel.com>
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-4690
Reviewed-on: http://review.whamcloud.com/9511


Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: James Simmons <jsimmons@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>