Bug 27048: Add basic timekeeping to rebuild_zebra

Bug 27048: Add basic timekeeping to rebuild_zebra

This patch adds a start time, end time and elapsed times on the 'records
exported' lines to the verbose output of the rebuild_zebra.pl script.

Test plan
1/ Run rebuild_zebra.pl -a -b -v
2/ Note the new timestamps included on the verbose output
3/ Signoff

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>