[libfabric-sarus branch] --skip-resource-manager flag still requires an ip & port in config

In the libfabric-sarus branch, the executor manager will crash if the resource_manager_address or resource_manager_port fields in config/executor_manager.json are not set. This crash still happens even when the executor manager is run with --skip-resource-manager. I can work on a fix at some point, but I just wanted to document the bug.

Code breaks here: https://github.com/spcl/rFaaS/blob/libfabric-sarus/server/executor_manager/manager.cpp#L28