LU-14786 lod: create missing debugfs file

LU-14786 lod: create missing debugfs file

While cleaning up debugfs symlinks the needed, but unused lod debugfs
directory was dropped. This results in the broken symlink

/sys/kernel/debug/lustre/lov/lustre-MDT0000-mdtlov

lctl params handling didn't see this due to glob returning only valid
directory entries so the error didn't get reported by stat(). Restore
the debugfs directory and add a new test to conf-sanity to detect any
potential breakage in the future.

Change-Id: I8fe0732d6caeeb83554833205998e24214343f88
Test-Parameters: env=ONLY=10a testlist=conf-sanity
Fixes: 462d476d ("LU-8066 obd: cleanup server sysfs symlinks handling")
Signed-off-by: James Simmons <jsimmons@infradead.org>
Reviewed-on: https://review.whamcloud.com/44113
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: John L. Hammond <jhammond@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>