CBQE-7274: Increase bucket size for backup examine tests

Magma has a minimum bucket size of 256MB, which is larger than the
previously used value of 100MB in couchstore. Increases the minimum to
allow for magma testing.

Change-Id: Ie7b1bce4091efe2158016c0957c9abcf52e6873a
Reviewed-on: http://review.couchbase.org/c/testrunner/+/162731
Tested-by: Joe Mitchell Jones <joe.mitchelljones@couchbase.com>
Reviewed-by: Jake Rawsthorne <jake.rawsthorne@couchbase.com>

pytests/ent_backup_restore/backup_examine_test.py

@@ -462,7 +462,7 @@ def populate_config(self):
         # The memory available on the node with the lowest memory
         self.config['memory'] = self.get_available_memory()
         # The size of each bucket that is created
-        self.config['bucket_size'] = 100
+        self.config['bucket_size'] = 256
         # The max buckets that can be created given the available memory and bucket size
         self.config['max_buckets'] = self.config['memory'] // self.config['bucket_size']