Run isRunning and isEnabled as sudo

[aileen]

closes #660
refs #414

Recently there were many users reporting issues when the CLI is running the command systemctl is-active. With the changes in #669 we are now able to run the isRunning and isEnabled methods in our systemd extension, as those were the only commands that weren't executed as sudo.

Manual tests worked fine for me. I can't say if it'll fix all the issues, as I wasn't able to reproduce the issues on the recommended stack. Nevertheless, there were enough reports of this issue actually happening on the recommended stack.

[coveralls]

Coverage remained the same at 100.0% when pulling df0bce1 on AileenCGN:sudo-systemd-isactive into c93124b on TryGhost:master.

[vikaspotluri123]

LGTM 👍

[acburdine]

So the isRunning part looks good, however the isEnabled part won't work quite right. When I converted the isRunning stuff to handle promises, I didn't convert the isEnabled code to handle them as well (see here and here). The reason this PR doesn't break anything is that the Promise returned by the isEnabled function technically is a truthy value, so the if statement in both those commands passes 🙈

I'll work on updating the isEnabled code as well, which should make this PR work as expected, but wanted to comment here first so it doesn't get merged before that's been done 😉

Edit: #674 has the other changes required for this PR to work.

[acburdine]

Tested this locally, works great :) thanks!