OPENDJ-2159 CR-7527 PDB Storage is read-only when using verify-index tool on Windows.

The real problem is the server is killed before flushing has a chance to run and the fact operations for tree creation
do not appear in the journal file. Adding a flag to open tree operations so that we can skip errors on missing trees
while the storage is read only.
Moreover, verify-index was trying to verify indexes already known to be in degraded state, and printing weird stats
about them.