LU-11003 ldlm: fix for l_lru usage

LU-11003 ldlm: fix for l_lru usage

Fixes for lock convert code to prevent false assertion and
busy locks in LRU:
- ensure no l_readers and l_writers when add lock to LRU after
  convert.
- don't verify l_lru without ns_lock.

Signed-off-by: Yang Sheng <yang.sheng@intel.com>
Change-Id: I8bcbdef3cb72db241ad03c50f5ce2b968e3ee3e4
Reviewed-on: https://review.whamcloud.com/32309
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>
Reviewed-by: Mike Pershin <mike.pershin@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>