- Move optimizer related tests, especially tests containing
  EXPLAINs of query plans, out of the ndb suite to a new
  ndb_opt suite
- ndb_opt is added to the list of default suites and the
  tests will be executed in ndbcluster runs in Server push
  build branches
- The tests are renamed to drop the "ndb_" prefix
- The ndb_charset test is moved to the ndbcluster suite
  (without the ndb_ prefix)
- Various small fixes such as cleaning up unused variables,
  unnecessary usage of include files, etc

Change-Id: I9141af2d9c52ce5eed95426e3e2467fe256d6fbe