Bug 17530: (QA follow-up) Replace our variable by cached value

Bug 17530: (QA follow-up) Replace our variable by cached value

Instead of saving the state locally in a variable during Plack lifetime,
we move the saved hash to the cache. We clear the key when we enter
smart-rules.pl. This makes a change in circ rules immediately effective.

Test plan:
Run the modified tests.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>