Make a clean distinction between Debian 7 and Debian 8.  Anticipate the
next Ubuntu LTS release (Xenial) that is planned for support.

Resolves #363.

Addresses #362.

refs #278

/etc/apache2/sites-available and old (dangling) symlinks in
/etc/apaches/sites-enabled.
Also, remove unnecessary apache2 restart after creating a new
virtualhost but not yet enabling it.

* Postfix: Trusty comes with postgresql 9.3, not 9.1
* owncloud 6.0.1 is part of the distribution, doesn't require opensuse repository
* owncloud requires libapache2-mod-php5
* uses prosody repository that matches the ansible_distribution_release (trusty, wheezy, etc)

The virtual site files must be owned by root (serious security issue)
and they must have the .conf filename suffix for a2ensite on
Ubuntu 14.04LTS (apache 2.4.7).

String-valued variables containing spaces can be substituted into an ansible
tasks file but they will not be interpreted correctly.

Remove all configuration for MySQL and configure PostgreSQL as the main
database.

All *_mysql_* options have been changed to *_db_* options.

Postgres requires the database user to have a password in order to
connect via localhost. The db_admin_password option is used to set the
password of the admin user (usually postgres).