test/abci: use random socket names to avoid collisions (#4885)
test/abci: use random socket names to avoid collisions (#4885)

Fixes these test failures:

```
=== RUN   TestKVStore
### Testing KVStore 
I[2020-05-25|13:32:31.303] Starting ABCIServer service                  module=abci-server impl=ABCIServer
    TestKVStore: example_test.go:48: 
                Error Trace:    example_test.go:48
                                                        example_test.go:28
                Error:          Received unexpected error:
                                listen unix test.sock: bind: address already in use
                Test:           TestKVStore
                Messages:       Error starting socket server
--- FAIL: TestKVStore (0.00s) 
```

tendermint/tendermint,tendermint/tendermint,tendermint/tendermint,tendermint/tendermint