Audio doesn't play from apps in LXD desktop container

[Michael Sheldon]

Steps to reproduce

1. Create a project with the following QML:

import QtQuick 2.4
import QtMultimedia 5.6
import Ubuntu.Components 1.3

MainView {
    applicationName: "audiotest.michael-sheldon"
    width: units.gu(100)
    height: units.gu(75)

    Page {
        header: PageHeader {
            title: i18n.tr("Audio Test")
        }

        MediaPlayer {
            source: "http://mikeasoft.com/~mike/dobro.ogg"
            autoPlay: true
        }
    }
}

2. Run it within an LXD desktop container

Expected result:

Audio should start playing

Actual result:

No audio can be heard