Track verify progress correctly

[mponomar]

Purely cosmetic.

Used to report:

  (out='verifying dtastripe 0, did 21743 records, 21743 per second')
  (out='verifying dtastripe 0, did 35642 records, 35642 per second')
  (out='verifying dtastripe 0, did 35720 records, 35720 per second')
  (out='verifying dtastripe 0, did 35814 records, 35814 per second')
  (out='verifying dtastripe 0, did 36350 records, 36350 per second')

Now reports:

 (out='verifying dtastripe 0, did 21743 records, 21743 per second')
 (out='verifying dtastripe 0, did 57385 records, 35642 per second')
 (out='verifying dtastripe 0, did 93105 records, 35720 per second')

ie totals are correctly cumulative

No specific test for this - but all tests run verify at the end.

[roborivers]

Cbuild submission: Error ⚠.
Regression testing: Success ✓.

The first 10 failing tests are:
cdb2jdbc
ssl_san
consumer_non_atomic_default_consumer_generated **quarantined**
manual_partition
ssl_set_cmd
ssl_prefer
ssl_dbname
sc_downgrade [timeout] **quarantined**