CDRIVER-2777 watch prefers readConcern from opts
CDRIVER-2777 watch prefers readConcern from opts

Don't use the collection's readConcern if there is a "readConcern" key
in "opts".

rcsanchez97/mongo-c-driver,acmorrow/mongo-c-driver,rcsanchez97/mongo-c-driver,mongodb/mongo-c-driver,beingmeta/mongo-c-driver,derickr/mongo-c-driver,mongodb/mongo-c-driver,beingmeta/mongo-c-driver,jmikola/mongo-c-driver,acmorrow/mongo-c-driver,mongodb/mongo-c-driver,jmikola/mongo-c-driver,rcsanchez97/mongo-c-driver,mongodb/mongo-c-driver,jmikola/mongo-c-driver,derickr/mongo-c-driver,derickr/mongo-c-driver,jmikola/mongo-c-driver,acmorrow/mongo-c-driver,mongodb/mongo-c-driver,beingmeta/mongo-c-driver,jmikola/mongo-c-driver,acmorrow/mongo-c-driver,rcsanchez97/mongo-c-driver,mongodb/mongo-c-driver,derickr/mongo-c-driver,beingmeta/mongo-c-driver,jmikola/mongo-c-driver,beingmeta/mongo-c-driver,derickr/mongo-c-driver,rcsanchez97/mongo-c-driver,beingmeta/mongo-c-driver,acmorrow/mongo-c-driver,jmikola/mongo-c-driver,rcsanchez97/mongo-c-driver,rcsanchez97/mongo-c-driver,beingmeta/mongo-c-driver,acmorrow/mongo-c-driver,derickr/mongo-c-driver,derickr/mongo-c-driver,acmorrow/mongo-c-driver,beingmeta/mongo-c-driver,mongodb/mongo-c-driver