ops must be reused in Awaited loops
ops must be reused in Awaited loops

test_http tickled this defect
op_ready throws Awaited after acquiring the op_slot.
receive() was destroying the op which was freeing op_slot.
When there were two ops waiting, the resulting put_nowait()
would release the other op, which would get the op_slot.
It would then throw Awaited, freeing op_slot. This caused
too many retries, and both ops died.

mrakitin/sirepo,radiasoft/sirepo,mrakitin/sirepo,mkeilman/sirepo,radiasoft/sirepo,radiasoft/sirepo,mrakitin/sirepo,radiasoft/sirepo,mkeilman/sirepo,mkeilman/sirepo,mkeilman/sirepo,radiasoft/sirepo,mrakitin/sirepo