Do not log rotate very small logs

Without this, after few weeks without use, each defined domain grows a
tail of empty gzipped logs, instead of keeping just the last log of
interest.

* daemon/libvirtd.logrotate.in: only rotate when the log is over 100 KBytes

(cherry picked from commit b03fe2d0aefb57a096a102bf23375f0a167ca189)

Fedora-patch: libvirt-logrotate-avoid-compressing-small-logs.patch