restore the dropped bits of 1c1bb85 and also implement the logic

suggested at
https://lists.linuxcontainers.org/pipermail/lxc-devel/2014-December/010985.html

Signed-off-by: S.Çağlar Onur <caglar@10ur.org>
Acked-by: Stéphane Graber <stgraber@ubuntu.com>

config/init/common/lxc-net.in

@@ -115,7 +115,15 @@ start() {
     if [ -n "$LXC_DOMAIN" ]; then
         LXC_DOMAIN_ARG="-s $LXC_DOMAIN -S /$LXC_DOMAIN/"
     fi
-    dnsmasq $LXC_DOMAIN_ARG -u lxc-dnsmasq --strict-order --bind-interfaces --pid-file="${varrun}"/dnsmasq.pid --conf-file=${LXC_DHCP_CONFILE} --listen-address ${LXC_ADDR} --dhcp-range ${LXC_DHCP_RANGE} --dhcp-lease-max=${LXC_DHCP_MAX} --dhcp-no-override --except-interface=lo --interface=${LXC_BRIDGE} --dhcp-leasefile=/var/lib/misc/dnsmasq.${LXC_BRIDGE}.leases --dhcp-authoritative || cleanup
+
+    # https://lists.linuxcontainers.org/pipermail/lxc-devel/2014-October/010561.html
+    for DNSMASQ_USER in lxc-dnsmasq dnsmasq nobody
+    do
+        if getent passwd ${DNSMASQ_USER} >/dev/null; then
+            break
+        fi
+    done
+    dnsmasq $LXC_DOMAIN_ARG -u ${DNSMASQ_USER} --strict-order --bind-interfaces --pid-file="${varrun}"/dnsmasq.pid --conf-file=${LXC_DHCP_CONFILE} --listen-address ${LXC_ADDR} --dhcp-range ${LXC_DHCP_RANGE} --dhcp-lease-max=${LXC_DHCP_MAX} --dhcp-no-override --except-interface=lo --interface=${LXC_BRIDGE} --dhcp-leasefile=/var/lib/misc/dnsmasq.${LXC_BRIDGE}.leases --dhcp-authoritative || cleanup
     touch "${varrun}"/network_up
     touch "${lockdir}"/lxc-net
 }