connman: fix build-time warning with sysvinit

connman: fix build-time warning with sysvinit

Due to recent modifications related to systemd, sysvinit builds began
to show this warning:

WARNING: connman-1.34-r0 do_package: connman: NOT adding alternative
provide /etc/resolv.conf: /etc/resolv-conf.connman does not exist

Fix this warning by making those updates specific to systemd.

Signed-off-by: Maxin B. John <maxin.john@intel.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>