t/jobs/t0012.fio: make this job time_based

t/jobs/t0012.fio: make this job time_based

From time to time we see failures (especially on Windows) with this test
because one of its jobs does not run long enough. Make the jobs run for
this test time_based so that they run for a minimum of 12s.

Example error output:

DEBUG:root:sample 0: job1 iops=343858.0 job2 iops=1719327.0 job3 iops=3438690.0 job3/job2=2.000 job3/job1=10.000
DEBUG:root:sample 1: job1 iops=682225.0 job2 iops=3411146.0 job3 iops=6822273.0 job3/job2=2.000 job3/job1=10.000
DEBUG:root:sample 2: job1 iops=1019335.0 job2 iops=5096697.0 job3 iops=10193375.0 job3/job2=2.000 job3/job1=10.000
DEBUG:root:sample 3: job1 iops=1367550.0 job2 iops=6837771.0 job3 iops=13675524.0 job3/job2=2.000 job3/job1=10.000
DEBUG:root:sample 4: job1 iops=1704137.0 job2 iops=8520706.0 job3 iops=17041393.0 job3/job2=2.000 job3/job1=10.000
DEBUG:root:sample 5: job1 iops=2056314.0 job2 iops=10281595.0 job3 iops=20563173.0 job3/job2=2.000 job3/job1=10.000
DEBUG:root:sample 6: job1 iops=2399343.0 job2 iops=11996744.0 job3 iops=23993468.0 job3/job2=2.000 job3/job1=10.000
DEBUG:root:Test 12 exception:
Traceback (most recent call last):
  File "D:\a\fio\fio\t\fiotestlib.py", line 465, in run_fio_tests
    test.check_result()
  File "D:\a\fio\fio\t\run-fio-tests.py", line 180, in check_result
    iops3 = iops3 + float(iops_files[2][i].split(',')[1])
Test 12 FAILED: list index out of range t0012.fio
IndexError: list index out of range

Signed-off-by: Vincent Fu <vincent.fu@samsung.com>