LU-8575 lod: clear ost usable flag to avoid striping.

LU-8575 lod: clear ost usable flag to avoid striping.

clear ost->ltd_qos.ltq_usable before checking
OBD_FAIL_MDS_OSC_PRECREATE param and some other flags in
lod_alloc_qos() while finding all ost's which are valid stripe
candidates. Call to lod_alloc_qos before setting this flag/param
sets ost->ltd_qos.ltq_usable to 1 for all valid ost but after
setting this flag/param ost->ltd_qos.ltq_usable not getting
cleared so there is need to clear it so that it will not get added
into stripe array.

Also in test_27u corrects problem where log file gets created in
lustre mount directory instead of /tmp. This make sures TLOG file
will not get created on ost0.

Seagate-bug-id: MRP-2847

Signed-off-by: Jadhav Vikram <jadhav.vikram@seagate.com>
Change-Id: I6dd16c44b331b09a0ffee530b3eb8508bde64294
Reviewed-on: http://es-gerrit.xyus.xyratex.com:8080/9757
Tested-by: Jenkins
Reviewed-by: Ujjwal Lanjewar <ujjwal.lanjewar@seagate.com>
Reviewed-by: Vladimir Saveliev <vladimir.saveliev@seagate.com>
Tested-by: Elena V. Gryaznova <elena.gryaznova@seagate.com>
Reviewed-on: http://review.whamcloud.com/22367
Reviewed-by: Yang Sheng <yang.sheng@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>
Reviewed-by: Niu Yawei <yawei.niu@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>