LU-6271 osc: further OSC cleanup after eviction

LU-6271 osc: further OSC cleanup after eviction

A few problems are fixed in this patch:
1. a ldlm lock could be canceled simutaneously by ldlm bl thread and
  cleanup_resource(). In this case, only one side will win the race
  and the other side should wait for the work to complete;
2. in lov_io_iter_init(), if cl_io_iter_init() against sub io fails,
  it should call cl_io_iter_fini() to cleanup leftover information;
3. define osc_lru_reserve() and osc_lru_unreserve() to reserve LRU
  slots in osc_io_write_iter_init() and unreserve them in fini();
4. eviction on group lock is well supported;
5. cleanups

Signed-off-by: Jinshan Xiong <jinshan.xiong@intel.com>
Change-Id: I293770b62e177a9ecefe0b4e05f3a8f44b1c831d
Reviewed-on: http://review.whamcloud.com/16456
Tested-by: Jenkins
Reviewed-by: Bobi Jam <bobijam@hotmail.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>