build_container: Allow pip to install system-wide

[RuoqingHe]

Summary of the PR

Found in https://github.com/rust-vmm/rust-vmm-container/actions/runs/13650154708/job/38156682477#step:7:2290.

We are having error: externally-managed-environment after upgrading to ubuntu:24.04. Remove EXTERNALLY-MANAGED file to allow pip to install packages system-wide.

And even if we have set -e, if pip install fails, the script goes on because we use the && operator.

Avoid this to make sure that we discover any errors with pip install.

Requirements

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[stefano-garzarella]

@RuoqingHe LGTM, just some notes about the commit message:

build_container: Avoid pip install with &&

Using pip install with bash && operator will cause failure of pip
install to escape from set -x, while we need this failure to be caught
by set -x.

Is set -e that will exit if a command fail. I suggest something like this:

build_container: Avoid pip install with &&

Even if we have `set -e`, if `pip install` fails, the script goes on because
we use the && operator.

Avoid this to make sure that we discover any errors with `pip install`.

[RuoqingHe]

build_container: Avoid pip install with &&

Even if we have set -e, if pip install fails, the script goes on because
we use the && operator.

Avoid this to make sure that we discover any errors with pip install.

Thanks for helping me with wording, I was struggling how to phrase this commit message 😂

[roypat]

ah nice, I was wondering how we ended up without pytest in the container haha