Tests for constants and Server/Manager execute methods

https://jira.mongodb.org/browse/PHP-1123
Please move this to LOAD_FIXTURES() so we can prep the test during SKIPIF (e.g. any pre-condition failures are caught in skipif and doesn't artificially fail the test "randomly").

I'm also thinking we should maybe import a small chunk of better test data.. say few hundred docs from enron dataset or something?