LP#1778783 - Circulate.pm fix log_me correct barcode var

LP#1778783 - Circulate.pm fix log_me correct barcode var

The log_me sub wasn't using the correct variable for showing the entered
barcode.  It should be $self->copy_barcode instead of $self->barcode.

Testing Notes:

Before fix:
1. Watch the logs with something like
  tail -f osrfsys.log | fgrep 'circulator: do_permit()'
2. Perform a checkout of a non-existant barcode.
3. Notice that the entered barcode is missing after 'copy='

After fix:
1. Restart the circ openils service
  osrf_control -l --service open-ils.circ --restart
2. Watch the logs.
3. Perform a checkout of a non-existant barcode.
4. Notice that the barcode is now shown after 'copy='

Signed-off-by: Josh Stompro <stompro@stompro.org>