The "with_extensions" variant currently uses --loadExtensions in resmoke to specify which extensions to load. A setup task in evergreen will populate a parameter "extension_paths" that is passed as a test flag in this variant.

With SPM-4363 changing extensions from being loaded from their shared library files to using a configuration file instead, the "with extensions" variant should do the same. 

This ticket should generate configuration files, populate "extension_paths" (renamed), and then delete the configuration files when the variant finishes.

Additionally, it would be nice to consolidate logic between this ticket and SERVER-110326, as they are similar.