base: Don't wait for swap devices in host-only mode.

base: Don't wait for swap devices in host-only mode.

The only reason we add swap devices to host-only mode (added in
dd5875499ece9dbc90e10eafd0073ee15d0c86a4) is to allow us to process
resume= arguments passed on the kernel command line when the swap
partition lives on something slightly more complex than a normal
partion (e.g. in an LVM or RAID setup).

By adding the device to host_devs, the necessary LVM and RAID hooks
are added and thus the underlying storage will be initialised OK, and
the 95resume module handles the waiting for the device (via udev rules
creating the /dev/resume symlink).

So ultimately, we do not need to hard-code the waiting for the swap
devices into the initramfs at build time as the waiting part can be
dynamic.

This makes things more resiliant to swap partitions disappearing and
being reformatted etc.

Inspired by a patch by Martin Whitaker on Mageia bug:
https://bugs.mageia.org/show_bug.cgi?id=12305