webadmin: Plugged Neutron agent backend code to frontend

Flush NeutronAgentBehavior fields when adding or editing provider,
init the fields from backend entity when editing existing provider.

Change-Id: I4ae42d320a761567e49aade7f6e104366e7e19c9
Signed-off-by: Lior Vernia <lvernia@redhat.com>