LU-4699 libcfs: unify ERR_PTR definitions

LU-4699 libcfs: unify ERR_PTR definitions

Add libcfs/err.h which either includes linux/err.h or defines
equiavlent functions (including ERR_CAST()) for use by userspace or
any of Lustre's other imaginary platforms. Modify the definition of
__container_of() to remove the pre-call explicit cast. Remove two
unused function that used container_of0() on an already dereferenced
pointer.

Signed-off-by: John L. Hammond <john.hammond@intel.com>
Change-Id: I26b454f835b51f1fb17b94eec7cf184f0a82071e
Reviewed-on: http://review.whamcloud.com/9519
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: wangdi <di.wang@intel.com>
Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>