Bug 26326: (follow-up) Add ability to check for existence of any primary key

Bug 26326: (follow-up) Add ability to check for existence of any primary key

Before dropping a primary key we need to see if one exists - this updates
the installer method to allow searching for existence of key

Signed-off-by: Andrew Fuerste-Henry <andrew@bywatersolutions.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Bug 26326: (follow-up) Address qa script failures

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