Apply Rusty Lynch's systemd socket activation feature.

Apply Rusty Lynch's systemd socket activation feature.

Add a new SCHEME for systemd's socket activation.
This patch already applied by Rusty Lynch, but before, I just discard it because of syncing with latest 2.2 code.
Now I apply his patch to secure-socket again with new SCHEME.

Please review this code and give me some better idea.

To use the socket-activation feature,
user should use "sdlocal://" scheme

practical example.

case #1. for secure-socket layer (the lowest layer)

int handle;
handle = secure_socket_create_server("sdlocal:///tmp/.sd.socket");

case #2. for com-core layer (the middle layer, which is merged with the g-main loop)
int handle;
handle = com_core_server_create("sdlocal:///tmp/.sd.socket", 0, service_cb, NULL);

case #3. for com-core_packet layer (the highest layer)
int handle;
handle = com_core_packet_server_init("sdlocal:///tmp/.sd.socket", method_table);

Change-Id: If62196bf0bea1855bf40f7fc71ea4b87e6d44dd5
Signed-off-by: Sung-jae Park <nicesj.park@samsung.com>