While fix for bug #1562713 changed the way how to save verification log in
case of some issues at CLI layer, it did not fixed old saved logs. Also, it
produced one more bug - IOError trace was saved as list instead of string.
This patch fixes the way of storage IOError and add migration to fix old data
Also, we change format of verification_log to dict here
Change-Id: Iffcf066e7033acd48f1446baebe0b2e9a334449f
Related-Bug: #1562713