LU-5044 mdd: do not return .lustre from readdir

LU-5044 mdd: do not return .lustre from readdir

In mdd_dir_page_build() skip dirents with the FID of .lustre
preventing that directory from being return by readdir on Lustre
clients. Add a sanity tets to this effect.

Signed-off-by: John L. Hammond <john.hammond@intel.com>
Change-Id: Ieecb77a286748c4bf4df4dee68d7f33670a0c286
Reviewed-on: http://review.whamcloud.com/11186
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: wangdi <di.wang@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>