python: rename 'venv-check' target to 'check-pipenv'

python: rename 'venv-check' target to 'check-pipenv'

Well, Cleber was right, this is a better name.

In preparation for adding a different kind of virtual environment check
(One that simply uses whichever version of Python you happen to have),
rename this test 'check-pipenv' so that it matches the CI job
'check-python-pipenv'.

Remove the "If you don't know which test to run" hint, because it's not
actually likely you have Python 3.6 installed to be able to run the
test. It's still the test I'd most prefer you to run, but it's not the
test you are most likely to be able to run.

Rename the 'venv' target to 'pipenv' as well, and move the more
pertinent help text under the 'check-pipenv' target.

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Willian Rampazzo <willianr@redhat.com>
Reviewed-by: Wainer dos Santos Moschetta <wainersm@redhat.com>
Message-id: 20210629214323.1329806-8-jsnow@redhat.com
Signed-off-by: John Snow <jsnow@redhat.com>