LU-10753 osd-zfs: initialize obj attr correctly

LU-10753 osd-zfs: initialize obj attr correctly

mdt_thread_info.mti_attr is used to initialize object attr in create,
currently it's copied to object.oo_attr directly, but some fields
in mti_attr may contain bogus data because it's not cleared in each
use, though la_valid is correctly set, but la_flags is used without
checking la_valid in __mdd_permission_internal().

Another minor fix in osd_create(): set size/nlink to zero since they
are set in valid.

Test-Parameters: testlist=sanity env=ONLY=300,ONLY_REPEAT=100

Signed-off-by: Lai Siyao <lai.siyao@whamcloud.com>
Change-Id: I64816b66a0b3c7aa50e62680d5251141697a8e0f
Reviewed-on: https://review.whamcloud.com/40062
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Alex Zhuravlev <bzzz@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Olaf Faaland-LLNL <faaland1@llnl.gov>
Reviewed-by: Mike Pershin <mpershin@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>