curl_global_init is not thread safe:
This function is not thread safe. You must not call it when any other thread in the program (i.e. a thread sharing the same memory) is running. This does not just mean no other thread that is using libcurl. Because curl_global_init calls functions of other libraries that are similarly thread unsafe, it could conflict with any other thread that uses these other libraries.
We should create a MONGO_INITIALIZER to initialize curl before we spawn threads in the database.