List a targets sub-targets/children from acquire using --list-children

[lhaagsma]

Added a new command line flag "--list-children" that from acquire's main function only returns a human readable list of child targets and exits.

Aims to close #239

Example output on Proxmox:

Listing children on Target: pve
- Found child #0: type=proxmox, path=/etc/pve/qemu-server/101.conf
- Found child #1: type=proxmox, path=/etc/pve/qemu-server/102.conf
- Found child #2: type=proxmox, path=/etc/pve/qemu-server/103.conf
- Found child #3: type=proxmox, path=/etc/pve/qemu-server/100.conf
- Found child #4: type=proxmox, path=/etc/pve/qemu-server/104.conf
Acquire finished successful

Acquire can be started with --child <#index> or . For Proxmox the VM name is not obvious as numbers are used. Will create a separate issue to parse these as part of the specific dissect loaders.