New option: require KVM. If false, Qemu VMs will not be prevented to run without KVM.

conf/gns3_server.conf

@@ -63,3 +63,5 @@ license_check = True
 [Qemu]
 ; !! Remember to add the gns3 user to the KVM group, otherwise you will not have read / write permssions to /dev/kvm !!
 enable_kvm = True
+; Require KVM to be installed in order to start VMs
+require_kvm = True