luci-base: read odhcpd leasefile location via uci
luci-base: read odhcpd leasefile location via uci

Check the location of the odhcpd leasefile from /etc/config/dhcp
via uci. Fallback to the default location.

This fixes #702

Signed-off-by: Hannu Nyman <ab53a3387de93e31696058c104e6f769cd83fd1b@iki.fi>
(cherry picked from commit 51a7f96877d8c5bf70217073ed8aa7ab6a196d20)

db260179/openwrt-bpi-r1-luci,db260179/openwrt-bpi-r1-luci,db260179/openwrt-bpi-r1-luci,db260179/openwrt-bpi-r1-luci,db260179/openwrt-bpi-r1-luci,db260179/openwrt-bpi-r1-luci,db260179/openwrt-bpi-r1-luci,db260179/openwrt-bpi-r1-luci