(replaces https://jira.mongodb.org/browse/SLS-527). In __btree_conf and probably other places in the code, we check if a btree is a stable file by explicitly checking against ".wt_stable".  Actually the code there is less robust, as it uses strstr. (We could get a false positive by creating table:foo.wt_stablexxx" It might be better to have a way to ask the block manager if the manager is for disagg.  String compares against uris should probably be avoided.