Revert "Start virtualbox VM one by one" because it doesn't fix the issue

This reverts commit da72a9501a.

gns3server/modules/virtualbox/__init__.py

@@ -41,9 +41,6 @@ class VirtualBox(BaseManager):
 
         super().__init__()
         self._vboxmanage_path = None
-        # It seem starting two VM in paralell can be an issue:
-        # https://github.com/GNS3/gns3-server/issues/190
-        self.start_lock = asyncio.Lock()
         self._execute_lock = asyncio.Lock()
 
     @property

gns3server/modules/virtualbox/virtualbox_vm.py

@@ -178,24 +178,23 @@ class VirtualBoxVM(BaseVM):
         if vm_state != "poweroff" and vm_state != "saved":
             raise VirtualBoxError("VirtualBox VM not powered off or saved")
 
-        with (yield from self.manager.start_lock):
-            yield from self._set_network_options()
-            yield from self._set_serial_console()
-
-            args = [self._vmname]
-            if self._headless:
-                args.extend(["--type", "headless"])
-            result = yield from self.manager.execute("startvm", args)
-            log.info("VirtualBox VM '{name}' [{id}] started".format(name=self.name, id=self.id))
-            log.debug("Start result: {}".format(result))
-
-            # add a guest property to let the VM know about the GNS3 name
-            yield from self.manager.execute("guestproperty", ["set", self._vmname, "NameInGNS3", self.name])
-            # add a guest property to let the VM know about the GNS3 project directory
-            yield from self.manager.execute("guestproperty", ["set", self._vmname, "ProjectDirInGNS3", self.working_dir])
-
-            if self._enable_remote_console and self._console is not None:
-                self._start_remote_console()
+        yield from self._set_network_options()
+        yield from self._set_serial_console()
+
+        args = [self._vmname]
+        if self._headless:
+            args.extend(["--type", "headless"])
+        result = yield from self.manager.execute("startvm", args)
+        log.info("VirtualBox VM '{name}' [{id}] started".format(name=self.name, id=self.id))
+        log.debug("Start result: {}".format(result))
+
+        # add a guest property to let the VM know about the GNS3 name
+        yield from self.manager.execute("guestproperty", ["set", self._vmname, "NameInGNS3", self.name])
+        # add a guest property to let the VM know about the GNS3 project directory
+        yield from self.manager.execute("guestproperty", ["set", self._vmname, "ProjectDirInGNS3", self.working_dir])
+
+        if self._enable_remote_console and self._console is not None:
+            self._start_remote_console()
 
     @asyncio.coroutine
     def stop(self):