network: do not write interface as 'auto' from ip= on command line.
When ip= on the kernel command line defines the networking, set
those network devices to be manually controlled, instead of 'auto'.
The reason for this is that if they're marked as 'auto':
a.) a second attempt will be made to ifup them.
b.) they'll be brought down on shutdown
'b' is problematic on network root filesystem.
Also this picks up 2 changes from curtin's net module:
- Cleanup newline logic so we always have a clean '\n\n' between stanza
- Add a unittest to validate bonding network config render, specifically
when to emit auto $iface for dependent bond slaves.