Mute false alarm when installing docker

In install_docker.sh, we will restart docker service, then connect
to /var/run/docker.sock with retry mechanism.

At the first contacting with /var/run/docker.sock, when docker
service is not ready, it may complain some error.

Mute this false alarm.

Change-Id: If00a18d2e3ddee951662e272d47ae84215f16ad2
Closes-Bug: #1252087
Neutron: Define a utility function to add neutron service class

When enabling neutron service (i.e. enable_service q-xxx), related code
unconditionally adds a necessary plugin class to Q_SERVICE_PLUGIN_CLASSES.
Which may cause duplication in Q_SERVICE_PLUGIN_CLASSES when
Q_SERVICE_PLUGIN_CLASSES is explicitly specified in localrc.
As a result, neutron server fails to start.

This patch introduces a utility function to add service class,
and check duplication.

Closes-Bug: #1261291
Change-Id: Id2880c7647babfccc3e8d9fc60dd93c4b3997ed9
Merge "Mute false alarm when installing docker"
Merge "Neutron: Define a utility function to add neutron service class"
Merge branch 'master' of github.com:openstack-dev/devstack