python/3.12 imp support

[jgphpc]

Hi,

It seems that python/3.12 removed imp:

https://docs.python.org/3/whatsnew/3.12.html

The asynchat, asyncore, and imp modules have been removed

which may explain why I get this error:

ERROR: failed to load configuration: could not load Python configuration file: 
'./cscs-reframe-tests/config/cscs.py': No module named 'imp'

reproduce with:

python -V # Python 3.12.3

python -m venv myvenv
source myvenv/bin/activate
pip install -r ~/reframe.git/requirements.txt
pip install hostlist

~/reframe.git/bin/reframe -C ./cscs-reframe-tests/config/cscs.py -c cscs-reframe-tests/checks/prgenv/ -l

ERROR: failed to load configuration: could not load Python configuration file: 
'./cscs-reframe-tests/config/cscs.py': No module named 'imp'

[jgphpc]

pip install hostlist is not needed (python-hostlist is but it works)