bug fix: UI set the network persistent attribute.

When create a network, start it and then stop it. It report this is
not a persistent network, it will delete it.

This is not right.

Every netowrk that kimchi create is persistent at present.

Js code should set the persistent attribute of network after a create
action.

Signed-off-by: ShaoHe Feng <shaohef@linux.vnet.ibm.com>