Added proper logrotate snipped for GlusterFS.

The current /etc/logrotate.d/glusterfs logrotate snipped, installed from
the glusterfs ebuild, sets some configuration options (such as weekly,
rotate etc.) in the globale scope, rather than in the GlusterFS log file scope.
This overwrites the user defined settings from /etc/logrotate.conf and
truns our rotation period from daily to weekly, resulting in huge log files :(
Apart from that, we prefer to use our global default values and have no need
for keeping rotated GlusterFS logs for 52(!) weeks.
Also see bug https://bugs.gentoo.org/show_bug.cgi?id=490672