LU-2267 osd-zfs: Use appropriate ZFS flags for file attributes

Instead of setting arbitrary bits in pflags, convert to use existing
ZFS attributes.  This format is different from previous implementation
and will cause older filesystems with attrs set to not behave
correctly.

Signed-off-by: Nathaniel Clark <nathaniel.l.clark@intel.com>
Change-Id: Ia0aac3e12adedd95b215f93ebe538a61abf910fa
Reviewed-on: http://review.whamcloud.com/5988
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>