LU-2924 Make quota namespace refcounting consistent

LU-2924 Make quota namespace refcounting consistent

It seems quota namespace is needlessly referenced on connect,
but that's not necessary as it could not go away until entire
obd goes away.
On the other hand this extra reference disturbs other logic
depending on empty namespace having zero refcount, so this patch
drops such extra referencing.

Change-Id: I62e04ef01a3673e4ffadc4204f3e1768e44fed18
Signed-off-by: Oleg Drokin <oleg.drokin@intel.com>
Reviewed-on: http://review.whamcloud.com/6234
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Niu Yawei <yawei.niu@intel.com>
Reviewed-by: Johann Lombardi <johann.lombardi@intel.com>