Running make inside a Guix Container From Outside

[jgart <jgart@dismail.de>]

Hi Guixers,

I started making a quick bash script that started like this:

```
#!/bin/sh
git clone https://git.savannah.gnu.org/git/guix.git guix-3000
cd guix-3000
guix environment guix --container
./bootstrap
./configure --local-statedir=/var
time make
exit
print "ready for hacking"
```

One of the problems with the above script is that the `guix environment guix --container` blocks `./bootstrap` etc...

I'm thinking of rewriting the script in python or guile using some form of async to solve that issue if needed.
Once `guix environment guix --container` is unblocked by me killing the process manually, 
the following commands run outside the container and fail. This is expected.

So, I ran `guix environment guix --container` in one terminal and opened another terminal to see if I can
first test running commands in containers from the "outside" with `guix container exec`.

I tried `guix container exec PID "./boostrap"` and it didn't fail. In the other terminal running the

container I looked to see if there was any change to container's directory structure and there was none.

I also ran `guix container exec PID "./configure --localstatedir=/var"` and
`guix container exec PID "time make"`.

Am I misusing `guix container exec`? 

Is it currently possible to run arbitrary commands in guix containers from outside guix containers?

all best,
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