Implements retry logic for getEntity and removes transaction.
Implements retry logic for getEntity and removes transaction.

The three "canary" tests landed in cl/363571136 pass 100% of the time when
run 10,000 times on rabbit with this patch applied.

PiperOrigin-RevId: 368322678

PolymerLabs/arcs,PolymerLabs/arcs,PolymerLabs/arcs,PolymerLabs/arcs,PolymerLabs/arcs,PolymerLabs/arcs,PolymerLabs/arcs,PolymerLabs/arcs