Summary
This ticket has multiple small tasks to improve code readability and code style. 

Acceptance Criteria (Definition of Done)

1. In "test/format/backup.c" there's this code: 

   trace_msg(session, "Backup #%u start%s%s%s", ++counter, config == NULL ? "" : ": (", config == NULL ? "" : config, config == NULL ? "" : ")"); 

   In other to improve readability we suggest changing it to something like this:

   if (config == NULL)
       trace_msg(session, "Backup #%u start", ++counter);
   else
       trace_msg(session, "Backup #%u start: (%s)", ++counter, config); 

1. There's no reason for "wt_wrap_open_session" and "wt_wrap_close_session" to be inline. Remove inline specifier for the method declarations.
2. Rename "test/format/ts.c" to "test/format/timestamp.c"
3. Make API names consistent in "test/format/ts.c". Here's a comment from Alex G: "I feel like the API naming in this file could be cleaned up a bit. I'd prefer to consistently use timestamp instead of mixing timestamp and ts. I'd also prefer if we could figure out a naming scheme that makes it practical to use it as a prefix rather than a suffix."