eval() is not a good idea. getattr is better.

But @will-Do , I have to say, this PR is not for the standard usage to control service.

We sugguest to use staging.service directly without anothor wrap of it. It is designed to meet this reqirement.  We can create a service in test script and start, stop or restart it. Wrap it in utils_net and expose an interface service_NetworkManager_control() seems no enhancement for it.

More information you can see disscution in https://github.com/autotest/virt-test/pull/1582 and https://github.com/autotest/virt-test/pull/1569 and https://github.com/autotest/virt-test/pull/1584