fix(ipmi_exporter): Fix privilege escalation when running in local mode

[netcho]

Fixes #526

[SkytAsul]

Would love to see this merged

[gardar]

The sudo policy should not be used for every installation of ipmi_exporter since it only applies to the local mode. Also, perhaps a better solution would be to just use root, since the sudo trickery won't work when using the Go-native IPMI implementation.