base-files: properly escape strings for version info

Make sure they don't break the sed command, and also make device_info
and openwrt_release more robust for parsing by scripts

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@41885 3c298f89-4303-0410-b956-a3cf2f4a3e73