LU-1365 tests: LARGEDIR and 3-level htree for local ldiskfs

LU-1365 tests: LARGEDIR and 3-level htree for local ldiskfs

Add conf-sanity.sh test for the LARGEDIR feature with Lustre + ldiskfs
to exceed both 2-level htree (with 1024-byte blocksize to reduce the
number of entries per htree level) and 2GB directory size (marked SLOW
since this takes a while to run). This is done using a smaller number
of hard-linked inodes (nlink_max = 65000), to avoid the overhead of
accessing and caching a large number of different inodes.

Running multiple threads on a single directory is serialized by the
VFS directory mutex, so the tests are run in parallel on all available
clients and mountpoints to speed up the test as much as possible.

Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Signed-off-by: Artem Blagodarenko <c17828@cray.com>
Change-Id: If52ef346a39a1c3236871edbb0327bf44fe1a392
Test-Parameters: trivial testlist=conf-sanity envdefinitions=SLOW=yes,FLAKEY=false
Reviewed-on: https://review.whamcloud.com/22009
Tested-by: Jenkins
Reviewed-by: James Nunez <jnunez@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>