Before:
node_openwrt_info{revision="r10756+1-7546be6007",model="GL.iNet GL-AR150",id="OpenWrt",board_name="glinet,gl-ar150",release="SNAPSHOT"} 1

After:
node_openwrt_info{revision="r10756+1-7546be6007",target="ath79/generic",board_name="glinet,gl-ar150",id="OpenWrt",model="GL.iNet GL-AR150",release="SNAPSHOT",system="Atheros AR9330 rev 1"} 1

Fixes #9730, replace #9735

Signed-off-by: Etienne Champetier <champetier.etienne@gmail.com>

Some releases may have non letters in it's name currently resulting in
an empty ("") output which is then discarded, resulting in *missing*
labels in the metric.

Now it uses `.-` to catch as little as possible, but anything.

Signed-off-by: Paul Spooren <mail@aparcar.org>

adds openwrt specific information about the device.
include DISTRIB_{ID, RELEASE, REVISION}, board_name and model

Example output:

    # TYPE node_openwrt_info gauge
    node_openwrt_info{revision="55a0636",model="QEMU Standard PC (i440FX + PIIX, 1996)",id="LiMe",board_name="qemu-standard-pc-i440fx-piix-1996",release="snapshot"} 1
    node_scrape_collector_duration_seconds{collector="openwrt"} 3.814697265625e-05
    node_scrape_collector_success{collector="openwrt"} 1

Signed-off-by: Paul Spooren <spooren@informatik.uni-leipzig.de>