Bug Fix #282: Disable Start/Stop network buttons while wait backend lag

When the user tries to Start/Stop (up/down) a network, there is a lag in
the backend, and it was possible to click on start/stop/delete again,
and again, generating errors. This patch disables the buttons and shows
loading gif to user, avoind this kind of error.

Signed-off-by: Rodrigo Trujillo <rodrigo.trujillo@linux.vnet.ibm.com>
Bug Fix #282: Handle toggleNetwork error returns

This patch restores the UI to previous state if function toggleNetwork
returns an error, when user tries to start/stop a network.

Signed-off-by: Rodrigo Trujillo <rodrigo.trujillo@linux.vnet.ibm.com>