block/005,008: do exit if fio did not finish within timeout

block/005,008: do exit if fio did not finish within timeout

In some bad situation, fio needs taking over several hours to complete
random read operations with specified size. The test may skip out in such
cases and does not block other cases run.

With this patch, the case will be ended within $TIMEOUT(if set) or 900s.
block/005 => nvme1n1 (switch schedulers while doing IO)      [failed]
    runtime      ...  1800.477s
    read iops    ...
    --- tests/block/005.out	2019-03-31 14:29:39.905449312 +0000
    +++ /home/ec2-user/blktests/results/nvme1n1/block/005.out.bad	2019-05-07 04:10:16.026681842 +0000
    @@ -1,2 +1,4 @@
     Running block/005
    +fio did not finish after 900 seconds which probably caused by
    +lower disk performance
     Test complete

Reviewed-by: Chaitanya Kulkarni <Chaitanya.Kulkarni@wdc.com>
Signed-off-by: Xiao Liang <xiliang@redhat.com>
[Omar: add some headroom for explicit timeouts]
Signed-off-by: Omar Sandoval <osandov@osandov.com>