Repair may miss some tablets that migrated across nodes.
So if tombstones expire after some timeout, then we can
have data resurrection.
Set default tombstone_gc mode to "repair" for tables which
use tablets (if repair is required).
Fixes: #16627.
Closesscylladb/scylladb#18013
* github.com:scylladb/scylladb:
test: check default value of tombstone_gc
test: topology: move some functions to util.py
cql3: statements: change default tombstone_gc mode for tablets