webadmin: Flush Neutron agent configuration when adding host

Plugged-in the backend code for the Network Provider section in Add
Host dialog. Also found out that QPID parameters aren't sent to the
backend on host installation, so disabled the UI fields.

Change-Id: I1b8d480a0913a0349298509f1a7770ddb0f03bc7
Signed-off-by: Lior Vernia <lvernia@redhat.com>