Catch error when the server as trouble to access to itself

Fix #940

gns3server/controller/__init__.py

@@ -16,6 +16,7 @@
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 import os
+import sys
 import json
 import socket
 import asyncio
@@ -68,6 +69,7 @@ class Controller:
             name = "Main server"
 
         computes = yield from self._load_controller_settings()
+        try:
             yield from self.add_compute(compute_id="local",
                                         name=name,
                                         protocol=server_config.get("protocol", "http"),
@@ -77,6 +79,9 @@ class Controller:
                                         user=server_config.get("user", ""),
                                         password=server_config.get("password", ""),
                                         force=True)
+        except aiohttp.web_exceptions.HTTPConflict as e:
+            log.fatal("Can't acces to the local server, make sure anything else is not running on the same port")
+            sys.exit(1)
         for c in computes:
             try:
                 yield from self.add_compute(**c)