t/verify.py: Add verify test script

t/verify.py: Add verify test script

The script contains three sets of tests. The first set of tests
exercises fio's decision making about checking the verify header's
sequence number and random seed. The second set of tests is aimed at
making sure that the checksum functions can detect data mismatches. The
final set of tests exercise fio's verify-related options such as
verify_backlog and verify_inteval.

This test script includes two checksum lists. The first list (default)
contains a subset of the checksum methods offered by fio, whereas the
second list contains the full set of checksum methods. The second, full
set can be run by specifying -c or --complete. Testing all of the
checksum methods can take a long time.

Signed-off-by: Vincent Fu <vincent.fu@samsung.com>
Signed-off-by: Ankit Kumar <ankit.kumar@samsung.com>