Fix & always include bin/activate in python & poetry plugin

[carlcsaposs-canonical]

Including bin/activate in the virtual environment will make debugging much easier (charm developers can easily run Python code using the charm's virtual environment to debug issues)

[carlcsaposs-canonical]

@lengau is this a change you want to include in charmcraft? so that the activate file works by default

or would it be better to include these commands manually in override-build, in case the format of the activate file changes in future python versions?
e.g.

    poetry-keep-bins: true
    override-build: |
      craftctl default
      # Remove venv/bin/ (included because `poetry-keep-bins: true`) except for venv/bin/activate
      shopt -s extglob
      rm -r "$CRAFT_PART_INSTALL/venv/bin/"!(activate)
      # Replace hard-coded path in `venv/bin/activate` with portable path
      # "\&" is escape for sed
      sed -i 's#^VIRTUAL_ENV=.*$#VIRTUAL_ENV="$( cd -- "$( dirname -- "${BASH_SOURCE[0]}" )/.." \&> /dev/null \&\& pwd )"#' "$CRAFT_PART_INSTALL/venv/bin/activate"

[lengau]

[lengau]

@carlcsaposs-canonical with the option to keep all the bins I think we can leave the activate script there just always (if someone really doesn't want it they can unstage it in the charm part). Thanks for the bash magic!

Could you fix the lint and the tests (make setup && make test-fast will get you the prerequisites and run the relevant tests)?

[carlcsaposs-canonical]

@lengau if keep bins is True, should we still modify bin/activate or leave it untouched?

[lengau]

@carlcsaposs-canonical let's just always modify it.

[lengau]

Thanks!