fix tsan errors on rayon

[spacejam]

• this could be real leaks... try to reproduce without coco and rayon in conjunction!
• this could be an issue with tsan handling fences in conjunction with coco
• this could be an issue in the sanitizer support implementation

[spacejam]

traced the errors to lazy_static rust-lang-nursery/lazy-static.rs#83

[spacejam]

muting these errors in rsdb CI by turning off the rayon feature flag, which sucks because we won't catch bugs introduced in rayon, but for now it lets us progress, and we'll periodically test rayon for tsan violations unrelated to lazy_static.