MINOR: checks: Add agent-addr config directive

This directive add possibility to set different address for agent-checks.
With this you can manage server status and weight from central place.

Can be backported to 1.7.
diff --git a/src/server.c b/src/server.c
index 0decb82..87452d3 100644
--- a/src/server.c
+++ b/src/server.c
@@ -1151,6 +1151,14 @@
 				newsrv->agent.inter = val;
 				cur_arg += 2;
 			}
+			else if (!strcmp(args[cur_arg], "agent-addr")) {
+				if(str2ip(args[cur_arg + 1], &newsrv->agent.addr) == NULL) {
+					Alert("parsing agent-addr failed. Check if %s is correct address.\n", args[cur_arg + 1]);
+					goto out;
+				}
+
+				cur_arg += 2;
+			}
 			else if (!strcmp(args[cur_arg], "agent-port")) {
 				global.maxsock++;
 				newsrv->agent.port = atol(args[cur_arg + 1]);