populus chain run should display th underlying geth command

* Populus Version: 1.4.0

### What was wrong?

It is not possible to know what kind of command populus chain run runs internally. This would be useful for diagnostics purposes.

#### Cute Animal Picture

```
o o (__) ^
\ / (oo) /
\ / _____\/___/
(__) \__/ / /\ / /
(oo) _______(oo) ^ / * /
/---------\/ /| ___ \/ / ___/
/ | x=a(b)|| / | { }|| *----/\
* ||------|| * ||{___}|| / \
^^ ^^ ||-----|| / /
^^ ^^ ^ ^

Mathematical Television This cow does Disco
Cow Cow (That's what comes of
(developer of (Cow-thode snorting cow-caine)
cow-culus) Ray Tube)
```

Start by locating the CLI implementation of `populus chain run` and tracing where it invokes geth. Verify the command's output before and after the change by running `populus chain run`; done means the underlying geth command is displayed clearly for diagnostics.

Written by the indexing model from the issue text.