Bug 23377: use ENV syspref override instead of complete disable

Bug 23377: use ENV syspref override instead of complete disable

In an attempt to save time, bulkmarcimport temporarily sets CataloguingLog
and AuthoritiesLog to 0.  It does this by disabling syspref caching and saving
the changes to the database (then replacing the original values at completion).

Unfortunately, this disables other key sysprefs from being cached, and results in
a 50% increase in processing time for the script.

This patch instead utilizes the ENV variable override feature of sysprefs, which
preempts the cache in C4::Context->preference().

To test:
1. Perform a bulkmarcimport with a reasonable number of biblios (~1000 will do)
2. Note the time taken to complete
3. Apply patch
4. Revert the biblio load performed
5. Perform another bulkmarcimport with the same biblios and commandline options
6. Note the time taken to complete
7. Compare times.  The time from step 6 should be about 33% less than the time from step 2
8. Check Cataloguing and Authorities Logs to verify imported records were not logged
9. Profit!

Signed-off-by: Michal Denar <black23@gmail.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>