packaging: log rotation - do not execute ls on non-existing files

Due to the usage of ls, ovirtlogrot.sh would print error messages if it
couldn't find any file matching the pattern engine.log.*
This patch removes the execution of ls, and therefore, removes the error
messages.

Change-Id: Icb3d443dd26c6e22302a694c1d0f433383f312b7
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=889751
Signed-off-by: Ofer Schreiber <oschreib@redhat.com>