core: Remove error message when reports.xml doesn't exist

WebAdmin requests the reports.xml file after login, and ServletUtils
prints an error message to the log if the file is not found. This
patch provides an option to hide error messages on unneeded files
that don't exist.

Change-Id: Iaf6b075eb4754c5bb4153da8c6032a01bf801516
Bug-Url: https://bugzilla.redhat.com/1060242
Signed-off-by: lzelkha@redhat.com <lzelkha@redhat.com>