Fix a crash when in some cases you can't access to VBOX state

Fix #137

gns3server/modules/virtualbox/virtualbox_vm.py

@@ -105,6 +105,7 @@ class VirtualBoxVM(BaseVM):
 
         results = yield from self.manager.execute("showvminfo", [self._vmname, "--machinereadable"])
         for info in results:
+            if '=' in info:
                 name, value = info.split('=', 1)
                 if name == "VMState":
                     return value.strip('"')