fix cache store instrumentation (logging) under Passenger
fix cache store instrumentation (logging) under Passenger

It turns out this setting is a thread-local variable, I'm guessing somebody
originally added it to debug specific requests.

test plan: This isn't really testable without running canvas inside of
Passenger. Basically, the "CacheStore" log lines should appear even when running
Canvas in Passenger.

Change-Id: I526514eeb1be15c70fecfaaf8acd6383e3c261b2
Reviewed-on: https://gerrit.instructure.com/56122
Reviewed-by: Kevin Blackham <1fab3aa4a150406f230c0d4557cd2d773ae8b3c5@instructure.com>
Reviewed-by: Cody Cutrer <c4fe2b1d90ef8f2548c8aeabfa633434316f0305@instructure.com>
Tested-by: Jenkins
QA-Review: August Thornton <9adc7a1161ddf32ff608de792a7e50179545f026@instructure.com>
Product-Review: Brian Palmer <3cb4e1df5ec4da2c7c4af7c52cec8cf340a55a10@instructure.com>

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