Create Missing Column Families

Summary: Provide an convenience option to create column families if they are missing from the DB. Task #4460490

Test Plan: added unit test. also, stress test for some time

Reviewers: sdong, haobo, dhruba, ljin, yhchiang

Reviewed By: yhchiang

Subscribers: yhchiang, leveldb

Differential Revision: https://reviews.facebook.net/D18951

include/rocksdb/options.h

@@ -595,6 +595,10 @@ struct DBOptions {
   // Default: false
   bool create_if_missing;
 
+  // If true, missing column families will be automatically created.
+  // Default: false
+  bool create_missing_column_families;
+
   // If true, an error is raised if the database already exists.
   // Default: false
   bool error_if_exists;