Bugfix#426: When no interface available, creating network popup error

V2 -> V3:
Change the align of "No interfaces found" that is aligned in another
line. Using ".show()", ".hide()" instead of "prop()".

V1 -> V2:
Add an indicator "(No interfaces found)" in "bridged" option under
Network tab when there exists no bridged interface.

This patch fix the the issue when creating a network that lack of
interface options pops up errors

Signed-off-by: Wen Wang <wenwang@linux.vnet.ibm.com>