lxc-net.in: fix failure executing dnsmasq

lxc-net.in: fix failure executing dnsmasq

Failure executing dnsmasq happens if misc dir is not existed as the
following error messages.

localhost.localdomain systemd[1]: Starting LXC network bridge setup...
localhost.localdomain lxc-net[5754]: dnsmasq: cannot open or create lease file /usr/local/var/lib/misc/dnsmasq.lxcbr0.leases: No such file or directory
localhost.localdomain dnsmasq[5754]: cannot open or create lease file /usr/local/var/lib/misc/dnsmasq.lxcbr0.leases: No such file or directory
localhost.localdomain dnsmasq[5754]: FAILED to start up
localhost.localdomain lxc-net[5727]: Failed to setup lxc-net.
localhost.localdomain lxc-net[5727]: Failed to setup lxc-net.
localhost.localdomain systemd[1]: lxc-net.service: Main process exited, code=exited, status=1/FAILURE
localhost.localdomain systemd[1]: lxc-net.service: Failed with result 'exit-code'.
localhost.localdomain systemd[1]: Failed to start LXC network bridge setup.

Modify 'lxc-net' script to call 'mkdir -p' command if the directory is not
existed before executing dnsmasq daemon.

Signed-off-by: Leesoo Ahn <lsahn@ooseel.net>