Log Message:
Update databases/mongo-c-driver to 1.2.0.

mongo-c-driver 1.2.0
- Much improved reporting of network errors, unavailable servers, and
  authentication failure
- Destroying an exhaust cursor must close its socket
- Various bugs in server reconnection logic
- mongoc_collection_aggregate returned invalid cursor after failure
- Wrong error message after failed network write on Sparc
- Missing JSON test files in release tarball
- Enable runtime asserts in release build.
- mongoc_client_kill_cursor is now deprecated and will be removed
  in version 2.0.

mongo-c-driver 1.1.11
- Undetected network errors when sending messages to the server
- Off-by-one error in mongoc_gridfs_file_seek with mode SEEK_END
- Memory leak parsing a URI that contains an invalid option