LU-4398 mdt: acquire an open lock for write or execute

LU-4398 mdt: acquire an open lock for write or execute

In mdt_object_open_lock() opens for write or execute will always
acquire an open lock of the appropriate mode so that any conflicting
cached open locks on other clients will be canceled. Add a regression
test to sanityn.sh.

Signed-off-by: John L. Hammond <john.hammond@intel.com>
Change-Id: I8092bca4c418ec99a25584abdfb635ffec19a26e
Reviewed-on: http://review.whamcloud.com/9063
Reviewed-by: Jinshan Xiong <jinshan.xiong@intel.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Mike Pershin <mike.pershin@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>