doltgresql can spoil future dolt runs in a subdirectory

After running `doltgresql` in a directory, if you then run `dolt` in that same directory (or a subdirectory), you will encounter this error:

```bash
% dolt sql
# Welcome to the DoltSQL shell.
# Statements must be terminated with ';'.
# "exit" or "quit" (or Ctrl-D) to exit.
dial tcp 127.0.0.1:5432: connect: connection refused
```

This happens because doltgresql leaves behind a server lock file that dolt uses to try to connect to it.

The two applications should produce different lock files and not attempt to consume each others.