Use pip install --force-reinstall flag

[pv]

Under some conditions, pip appears to wrongly think the packages is
available in the environment, so tell it to install it always.

Closes #805

In the problematic case asv run -v says

·· Running 'xxx/python -mpip install /home/pauli/tmp/xxx/requests/.asv/env/a80b4bcff004e7d21aafa78a5932418b/asv-build-cache/9742da7f91f595796a412a8150aacc00191be039/requests-2.21.0-py2.py3-none-any.whl'
   OUTPUT -------->
   Requirement already satisfied: requests==2.21.0 from file:///xxx/requests/.asv/env/a80b4bcff004e7d21aafa78a5932418b/asv-build-cache/9742da7f91f595796a412a8150aacc00191be039/requests-2.21.0-py2.py3-none-any.whl in xxx/requests/.asv/env/a80b4bcff004e7d21aafa78a5932418b/project (2.21.0)

But I don't know precisely why this occurs (hence no test). However, adding the --force-reinstall flag appears to fix it.

[yashasvi-goel]

I'm facing a similar issue.
I've tried this solution(#805 #806 ). It isn't solving the issue for me. I've tried updating my pip as well.
I've double checked my asv.conf.json. Is there any other solution to fix this issue.