Allow full validation to retry verify until it is successful, either with a new parameter, or as the default.

Validate {full: true} runs WT verify on each collection and index table. However, if the table is actively being used, WT will return EBUSY, and validate skips the table and moves on. This means that we have no way to ensure the table has been verified at the WT-level.

Why does this happen?
Full collection validate uses a collection X lock to block writers, but internal background threads that use lock-free reads will not conflict with the validate command and prevent WT from obtaining exclusive access on the underlying table.

In practice, we perform validation offline and in standalone mode, however, the current behavior makes it hard for us to make a guarantee about WT-level data integrity, which we want to improve.