Only configure Neutron DB connection if it is set

The Neutron ml2 agent does not require access to the database.
This patch avoids configuring the database/connection setting
if no metadata is present.

Change-Id: If584b153e8ded71e63be129b62cecd7544aabb07
Disable set -x for passwords

When we are interacting with passwords we should disable logging.

Closes-Bug: #1298205

Change-Id: I101db98c4be9d8c865b7457474a483fedebf281c
Merge "Disable set -x for passwords"
Merge "Only configure Neutron DB connection if it is set"