LU-7404 zfs: reset ZFS baseline to 0.6.4.2

LU-7404 zfs: reset ZFS baseline to 0.6.4.2

ZFS 0.6.5.2 is known to introduce I/O problems with the following
stack backtrace:

Call Trace:
 [] ? vdev_mirror_child_done+0x0/0x30 [zfs]
 [] io_schedule+0x73/0xc0
 [] cv_wait_common+0xaf/0x130 [spl]
 [] ? autoremove_wake_function+0x0/0x40
 [] __cv_wait_io+0x18/0x20 [spl]
 [] zio_wait+0x10b/0x1e0 [zfs]
 [] dbuf_read+0x439/0x850 [zfs]
 [] __dbuf_hold_impl+0x1a1/0x4f0 [zfs]
 [] dbuf_hold_impl+0x7d/0xb0 [zfs]
 [] dbuf_hold+0x20/0x30 [zfs]
 [] dmu_buf_hold_noread+0x87/0x140 [zfs]
 [] dmu_buf_hold+0x3b/0x90 [zfs]
 [] ? dbuf_rele_and_unlock+0x268/0x400 [zfs]
 [] zap_lockdir+0x5a/0x770 [zfs]
 [] ? kmem_cache_alloc_node_trace+0x1cd/0x200
 [] zap_lookup_norm+0x4a/0x190 [zfs]
 [] zap_lookup+0x33/0x40 [zfs]
 [] dmu_tx_hold_zap+0x146/0x210 [zfs]
 [] osd_declare_object_create+0x2a5/0x440 [osd_zfs]
 [] ofd_precreate_objects+0x4e4/0x19d0 [ofd]
 [] ? libcfs_debug_msg+0x41/0x50 [libcfs]
 [] ? ofd_grant_create+0x23b/0x3e0 [ofd]
 [] ofd_create_hdl+0x56e/0x2640 [ofd]
 [] ? lustre_pack_reply_v2+0x220/0x280 [ptlrpc]
 [] tgt_request_handle+0x8bc/0x12e0 [ptlrpc]
 [] ptlrpc_main+0xe41/0x1910 [ptlrpc]
 [] ? ptlrpc_main+0x0/0x1910 [ptlrpc]
 [] kthread+0x9e/0xc0
 [] child_rip+0xa/0x20
 [] ? kthread+0x0/0xc0
 [] ? child_rip+0x0/0x20

Signed-off-by: Jinshan Xiong <jinshan.xiong@intel.com>
Change-Id: Ia10427523535ba82cc374e2eae52014cadfac0de
Reviewed-on: http://review.whamcloud.com/17712
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Nathaniel Clark <nathaniel.l.clark@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>