Log Message:
coturn: Merge improvements from wip

This is step 2 of the three-way merge of wip and net.

  - Set up a non-root user/group and tell the daemon to run as that
    user, avoiding it staying as root.
  - Use 'coturn' as the package name consistently, because upstream
    releases the package coturn containing the program turnserver.
    The package name is used for example/doc directories and the
    user/group.
  - Respect PKG_SYSCONFDIR harder, not letting coturn default to
    $prefix/etc, and use PKG_SYSCONFDIR in the rc.d script.
  - Simplify CONF_FILES handling, as upstream already installed the
    example in $egdir as just turnserver.conf.  Rather than moving
    .conf.example from etcdir to egdir, just remove, and then have
    CONF_FILES use the example.
  - add comment about a database installed in .destdir/var -- which
    doesn't get picked up by the package but still seems wrong.