MRP-1658 test: add failback test with errors=panic

This is test for MRP-1658 which create activity and
emulate failback operations. Option errors=panic
is using similar to production servers. Test requires
ENABLE_QUOTA=yes option.

Signed-off-by: Alexander Boyko <alexander_boyko@xyratex.com>
Change-Id: Iae6765b747ff266e6a44df8ebcd48cfba1991837
Reviewed-on: http://es-gerrit.xyus.xyratex.com:8080/1550
Tested-by: Jenkins
Tested-by: Elena Gryaznova <elena_gryaznova@xyratex.com>
Reviewed-by: Elena Gryaznova <elena_gryaznova@xyratex.com>
Reviewed-by: Andrew Perepechko <andrew_perepechko@xyratex.com>
Reviewed-by: Vitaly Fertman <vitaly_fertman@xyratex.com>
MRP-1658 ldiskfs: skip checking in readonly mode

During umount ext4_mb_release_inode_pa()->ext4_error() panic, cause
memory bitmap and on-disk bitmap are different. This happened because
umount use Lustre readonly mode.
ext4_error() function could panic on errors if no MS_RDONLY.
But for the Lustre, readonly mode should be checked with
dev_check_rdonly() function. This patch skip total check at
ext4_mb_release_inode_pa() for readonly, like it was before,
but slightly early. So ext4_error() could not be called.

Signed-off-by: Alexander Boyko <alexander_boyko@xyratex.com>
Change-Id: Ia9471b97186db41195c147f70fa871b7283e5fed
Reviewed-on: http://es-gerrit.xyus.xyratex.com:8080/1534
Tested-by: Jenkins
Reviewed-by: Andrew Perepechko <andrew_perepechko@xyratex.com>
Reviewed-by: Alexey Lyashkov <alexey_lyashkov@xyratex.com>
Tested-by: Elena Gryaznova <elena_gryaznova@xyratex.com>
Reviewed-by: Vitaly Fertman <vitaly_fertman@xyratex.com>