rust: rmeta files are hashed as well
rust: rmeta files are hashed as well

Summary:
`.rmeta` files, generated by `#check` flavoured builds, also contain
a metadata hash, so make sure we handle that.

Test Plan: unit tests

Reviewed By: andrewjcg

fbshipit-source-id: 15ca886

ilya-klyuchnikov/buck,JoelMarcey/buck,brettwooldridge/buck,zpao/buck,SeleniumHQ/buck,clonetwin26/buck,brettwooldridge/buck,Addepar/buck,SeleniumHQ/buck,SeleniumHQ/buck,LegNeato/buck,JoelMarcey/buck,romanoid/buck,JoelMarcey/buck,shs96c/buck,Addepar/buck,brettwooldridge/buck,ilya-klyuchnikov/buck,clonetwin26/buck,SeleniumHQ/buck,clonetwin26/buck,facebook/buck,rmaz/buck,romanoid/buck,SeleniumHQ/buck,shs96c/buck,romanoid/buck,brettwooldridge/buck,Addepar/buck,ilya-klyuchnikov/buck,clonetwin26/buck,LegNeato/buck,romanoid/buck,brettwooldridge/buck,zpao/buck,romanoid/buck,JoelMarcey/buck,nguyentruongtho/buck,kageiit/buck,LegNeato/buck,JoelMarcey/buck,shs96c/buck,ilya-klyuchnikov/buck,SeleniumHQ/buck,rmaz/buck,ilya-klyuchnikov/buck,clonetwin26/buck,kageiit/buck,Addepar/buck,rmaz/buck,JoelMarcey/buck,ilya-klyuchnikov/buck,Addepar/buck,shs96c/buck,rmaz/buck,ilya-klyuchnikov/buck,ilya-klyuchnikov/buck,rmaz/buck,ilya-klyuchnikov/buck,shs96c/buck,zpao/buck,kageiit/buck,shs96c/buck,nguyentruongtho/buck,romanoid/buck,shs96c/buck,JoelMarcey/buck,LegNeato/buck,shs96c/buck,JoelMarcey/buck,SeleniumHQ/buck,LegNeato/buck,LegNeato/buck,SeleniumHQ/buck,brettwooldridge/buck,zpao/buck,LegNeato/buck,brettwooldridge/buck,LegNeato/buck,brettwooldridge/buck,rmaz/buck,JoelMarcey/buck,SeleniumHQ/buck,romanoid/buck,romanoid/buck,SeleniumHQ/buck,zpao/buck,JoelMarcey/buck,nguyentruongtho/buck,clonetwin26/buck,romanoid/buck,Addepar/buck,ilya-klyuchnikov/buck,ilya-klyuchnikov/buck,romanoid/buck,clonetwin26/buck,kageiit/buck,rmaz/buck,Addepar/buck,kageiit/buck,ilya-klyuchnikov/buck,clonetwin26/buck,LegNeato/buck,facebook/buck,clonetwin26/buck,LegNeato/buck,shs96c/buck,brettwooldridge/buck,Addepar/buck,zpao/buck,rmaz/buck,romanoid/buck,Addepar/buck,rmaz/buck,SeleniumHQ/buck,brettwooldridge/buck,kageiit/buck,facebook/buck,facebook/buck,clonetwin26/buck,facebook/buck,brettwooldridge/buck,rmaz/buck,rmaz/buck,shs96c/buck,clonetwin26/buck,Addepar/buck,brettwooldridge/buck,nguyentruongtho/buck,zpao/buck,LegNeato/buck,LegNeato/buck,romanoid/buck,nguyentruongtho/buck,shs96c/buck,SeleniumHQ/buck,kageiit/buck,JoelMarcey/buck,rmaz/buck,Addepar/buck,Addepar/buck,clonetwin26/buck,shs96c/buck,rmaz/buck,Addepar/buck,SeleniumHQ/buck,ilya-klyuchnikov/buck,JoelMarcey/buck,nguyentruongtho/buck,facebook/buck,nguyentruongtho/buck,facebook/buck,clonetwin26/buck,JoelMarcey/buck,LegNeato/buck,romanoid/buck,brettwooldridge/buck,shs96c/buck