utils: Cleanup command logging

A new dictionary was created for selecting the "SUCCESS" or "FAILED"
message for the debug log. This is pointless when debug messages are not
logged. Replaced with nicer and probably more efficient conditional
expression.

repr(err) was invoked even when debug messages are not logged. Use now
%r format, so conversion is done only when log message is formatted.

Change-Id: Ia5cbe6c380a5427dd69a3efbceea4ea8e35783ab
Signed-off-by: Nir Soffer <nsoffer@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/27757
Reviewed-by: Dan Kenigsberg <danken@redhat.com>