auto-installer: add auto-installer binary

auto-installer: add auto-installer binary

It expects the contents of an answer file via stdin. It will then be
parsed and the JSON for the low level installer is generated.

It then calls the low level installer directly.
The output of the installaton progress is kept rather simple for now.

If configured in the answer file, commands will be run pre and post the
low level installer.

It also logs everything to the logfile, currently
'/tmp/auto_installer.log'.

Tested-by: Christoph Heiss <c.heiss@proxmox.com>
Reviewed-by: Christoph Heiss <c.heiss@proxmox.com>
Signed-off-by: Aaron Lauterer <a.lauterer@proxmox.com>
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>