Add 'secret' property for 'connection' option

Neutron cli registers 'connection' option without
'secret=True' property. This commit makes sure
'connection' option has 'secret' property when
it is registered.

Change-Id: I0b0a5aca44a8eeee1c12513f30b9559f1d008442
Closes-Bug: #1319651
Merge "Add 'secret' property for 'connection' option"