hooks/archiso: use resolve_device() instead of poll_device()

nl6720requested to merge
nl6720/mkinitcpio-archiso:use-resolve_device into master

Unlike poll_device, resolve_device supports using tags (e.g. UUID=, LABEL=, PARTUUID=, PARTLABEL=) to specify a device. This is a lot more prettier than using the /dev/disk/by-*/* symlinks.

Since mount supports these tags, they can be passed to it as is.

Implements #10 (closed)

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