webadmin: Discover Network

Added discover networks popup window, in which a provider's network may
be discovered and then chosen to be imported into a data center. This
will be triggered from a button in the Provider/Networks subtab.

Change-Id: I438c806a341742bd97a9d0948764007061354204
Signed-off-by: Alona Kaplan <alkaplan@redhat.com>