Bug 9049: Don't use shadow with rebuild_zebra -r

Bug 9049: Don't use shadow with rebuild_zebra -r

Due to a limitation of Zebra, the register must be cleared *before*
doing shadow indexing if you want to reset the indexes. In light of
that, it does not make sense to do shadow indexing at all when
rebuild_zebra.pl is run with the -r switch. This patch makes -r (reset)
imply -n (no shadow).

To test:
1) Run `rebuild_zebra.pl -b -r -v -v -v`
2) Note that the script never runs the merge phase

Without the patch I see log lines refering to the shadow cache (enabling shadow spec=/home/koha/koha-dev/var/lib/zebradb/biblios/shadow:20G)
With the patch I don't see anything in the logs about shadow.  I do however see lines about merging.  I think it could just be a misunderstanding of the logs

Signed-off-by: wajasu <matted-34813@mypacks.net>
Signed-off-by: Elliott Davis <elliott@bywatersolutions.com>
Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>