LU-6765 obdecho: don't copy lu_site

LU-6765 obdecho: don't copy lu_site

While creating an echo device, echo_device_alloc() copies the lu_site
from MD stack, such kind of copy result in uninitialized mutex and
other potential issues.

Instead of copying the lu_site, we'd use the lu_site by pointer directly.

Test-Parameters: alwaysuploadlogs envdefinitions=SLOW=yes \
mdtfilesystemtype=zfs mdsfilesystemtype=zfs ostfilesystemtype=zfs \
clientdistro=el6.6 ossdistro=el6.6 mdsdistro=el6.6 \
mdtcount=1 testlist=mds-survey

Test-Parameters: alwaysuploadlogs envdefinitions=SLOW=yes \
mdtfilesystemtype=ldiskfs mdsfilesystemtype=ldiskfs ostfilesystemtype=ldiskfs \
clientdistro=el6.6 ossdistro=el6.6 mdsdistro=el6.6 \
mdtcount=1 testlist=mds-survey

Signed-off-by: Niu Yawei <yawei.niu@intel.com>
Signed-off-by: Olaf Faaland <faaland1@llnl.gov>
Change-Id: I00bd1a211cf0d556e427ba2f281fbcb1940d41f3
Reviewed-on: http://review.whamcloud.com/15657
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Bobi Jam <bobijam@hotmail.com>
Reviewed-by: Lai Siyao <lai.siyao@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>