Install libasound2-plugins before CRAS, so the ALSA config is written.
Install libasound2-plugins before CRAS, so the ALSA config is written.

libasound2-plugins creates /etc/alsa/conf.d (newer) or
/usr/share/alsa/alsa.conf.d (older), which targets/audio needs in
order to write the config file that defines the 'cras' device
(10-cras.conf).

Fixes #2925.

dnschneid/crouton,dnschneid/crouton,dnschneid/crouton,dnschneid/crouton,dnschneid/crouton,dnschneid/crouton