[build] Use python -m pip workaround

[build] Use python -m pip workaround

pipenv depends on pip, which conflicts with some distro versions of
pip, see bug [1].

While at it, workaround lib64 issues on CentOS by passing
`--always-copy` when creating the venv [2].

[1] https://github.com/pyenv/pyenv/issues/1141
[2] https://github.com/pypa/pipenv/issues/1929

Change-Id: I6af1a5fdbe8d37f75ab8b09b050449ad432191ad
Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>
(cherry picked from commit 54164b84abc2b6b8772d2ac083e11ce7c137cc7c)