Support for modular libvirt daemons

Currently the socket is defined as a variable here https://github.com/digitalocean/go-libvirt/blob/15feff002086ca5276717d866e19ebf9e082f343/socket/dialers/local.go#L10

so it only works with **Monolithic daemon** mode (libvirtd) and not the **Modular daemons** mode (virtqemud, virtstoraged,...).

Ref: https://libvirt.org/daemons.html

Start with socket/dialers/local.go, especially the socket variable referenced in the issue, and read the linked libvirt daemon documentation to understand modular socket names. Done means the local dialer supports modular daemons such as virtqemud and virtstoraged while retaining support for monolithic libvirtd.

Written by the indexing model from the issue text.