Clean up python ts object creation.

Clean up python ts object creation.
- Remove code duplication by making rpmts_Create() just a wrapper that calls
  rpmtsObject to create the instance
- Move the initialization from rpmts_init() to rpmts_new(), calling
  ts.__init__() multiple times isn't something we want to allow (setting
  vsflags multiple times is ok but there's a method to do that already)